That at least is the suggestion of the South Korean intelligence agency as it scrambles to recover from the embarrassment of not finding out about Kim's death until it was announced by North Korean state television two days and three hours later.

While official reports had him expiring from ''great mental and physical strain'' aboard a train on his way to give his trademark ''on-the-spot guidance'' at factories and army foxholes, satellite imagery does not show Kim's special train on the move at the time. He probably died in one of his many palatial homes.

When Kim's body is taken to its tomb on Wednesday, past ranks of goose-stepping soldiers and sobbing civilians massed in Pyongyang, an even wider divergence between heroic myth and prosaic reality will remain. According to the official legend, Kim was born in a cabin in February 1942 on the semi-sacred Mount Paektu in the country's far north, from where his father, Kim Il-sung, was leading a fierce guerilla campaign against the occupying Japanese across Korea and Manchuria. But Russian records say he was born a year earlier in a village near the city of Khabarovsk, where the father was being sheltered and trained by the Soviet army for his eventual return to Korea after the Japanese surrender.

The myths of the Kim guerilla dynasty are not being discarded but actually strengthened as this contemporary version of the ancient Korean ''hermit kingdom'' moves into succession by the third generation. The chosen ''Great Successor'' - Kim Jong-il's third son, Kim Jong-un - was consciously picked by his ailing father as a political throwback, one who would not change the rigid political system but intensify its hereditary personality cult even further.

In 2003 a Japanese sushi chef, one of a succession of cooks imported to serve Kim Jong-il's famous epicurism amid the endemic starvation among the North Koreans, reported that the youngest son exhibited suspicion and a ''glaring ferocity'' towards strangers, notes Bradley Martin, author of the compendious study of the Kim dynasty, Under the Loving Care of the Fatherly Leader.

''All we know is what the sushi chef told us: he's the meanest and most aggressive of the children,'' Martin elaborated by phone this week. ''And that's why Kim Jong-il liked him. We have to assume he was chosen because of hope that he would continue the old policies.''

Moreover, the chubby-faced son looks uncannily like his grandfather, Kim Il-sung, which Martin and many other analysts think is being played up. ''He's got the same haircut his grandfather had when he made that speech in 1945 right after the Soviets brought him back - a critic at the time wrote disparagingly of this 'Chinese waiter's haircut' - and he wears the old-style Mao tunics,'' Martin said. ''There's even rumours he's had plastic surgery. They do have a big plastic

surgery operation at the hospital where the elite go in Pyongyang: they use it for agents to make them prettier or more handsome so they can seduce people abroad. That is branding, because they all knew that the father was not popular. They are hoping this kid will revive memories of the glory days, such as they were.''

Kim Jong-un emerged as the heir apparent, given a four-star general's rank in the 1.1 million-strong Korean People's Army and taken on his father's visits to China and Russia to be introduced, after Kim Jong-il's severe stroke in August 2008 telescoped what would otherwise have been a more careful preparation to succeed - like Kim Jong-il's own nomination in 1981, 13 years before Kim Il-sung died.

But already the more obvious successor had been knocked out. Oldest son Kim Jong-nam had caused great embarrassment in 2001 when he was caught taking a family group into Japan on fake Dominican Republic passports - to visit Tokyo Disneyland. He dropped out of Pyongyang circles and since then has spent much of the time pursuing business interests in China and Macau.

This was a convenient excuse for his father, say some specialists. Kim Jong-il had spent his early career known as the shadowy ''Party centre'' enforcing orthodoxy on Kim Il-sung's ''Juche'' (Self-Reliance) development ideology. Then in power himself, he had pushed the Korean Workers' Party to one side, and proclaimed a ''Songun'' (Army First) strategy - in recent years amending the constitution to make the National Defence Commission the supreme authority and its chairman (himself) the country's top leader.

According to Russian officials like General Konstantin Pulikovsky, who travelled with Kim on his long train trips to Moscow (he hated flying), Kim could never be persuaded to think beyond centralised planning and heavy industry, the classic Leninist-Stalinist model. ''Kim Jong-il would always say something like North Korea can't be a capitalist country because it's a small country,'' says Leonid Petrov from Sydney University, a Korea scholar trained at the Institute of Oriental Studies in St Petersburg.

Worse than the Disneyland gaffe, the oldest son was showing signs of wanting to change the system.

''It is said that Kim Jong-nam lost favour because he had conflicting ideas with his father on national development and was not satisfied with his father's Songun policies and his provocative and confrontational external policies,'' says Cai Jian, a professor specialising in north-east Asia at Shanghai's Fudan University.

''There were reports to say that he was indiscreet and told his friends if he took power he'd reform the economy,'' Martin also heard. ''He is very close with the Chinese. He would have been their choice for the job.'' Indeed, US diplomatic cables from China, revealed by WikiLeaks, show Chinese officials reluctant to acclaim the younger son at first.

Still, Kim Jong-un is only somewhere between 27 and 29, and little is known about his upbringing except for a short spell at a private school in Switzerland. Can he really develop into a strong leader in his own right? Or will he be a figurehead while factions and contenders emerge from the army, the party, the bureaucracy, and the Pyongyang elite?

Petrov says it could be anything up to three years before it becomes clear, with the appointment of the chairman of the National Defence Commission to replace Kim Jong-il. The second in charge at present , as first vice-chairman, is the brother-in-law of the dead leader, Jang Song-taek, an urbane 65-year-old with military and Chinese connections as well as his dynastic link through marriage to Kim's sister, Kim Kyong-hui. The couple are mentors to the successor, and Jang could become effectively a regent.

''We will have to see who is going to become the commission's chairman,'' Petrov says. ''If it's Jang it's going be a kind of collective leadership, but if Kim Jong-un becomes chairman, this would put Jang and other military in the second position. I am not sure it will be done immediately. They might keep this post empty for one, two or three years, like it was in the mourning period after Kim Il-sung died.''

Cai says the son has already begun promoting younger cadres in the military since his elevation. Older officers are said to call him ''the little boy'' but Cai doubts they would dare to put him down. ''It is still unknown how much political energy these people have and how much threat they could bring,'' he says. ''There is no one figure with prestige and popularity in North Korea to compete against him.''

China has meanwhile swung its diplomatic effort into building a relationship with Kim Jong-un in the hope of avoiding the kind of nasty surprises like nuclear tests and ballistic missile firings that came from his father.

''What China hopes for most is the presence of a pro-China government on the peninsula,'' Cai says. ''If not a pro-China government, at least it should be non- pro-United States, otherwise China will regard it as a potential strategic threat. The existence of North Korea is just to maintain such leverage - it's not about Kim Jong-il or Kim Jong-un.''

The hope is that by showing strong support to the new leader now, Beijing can build its influence. ''China's mainstream opinion is to strengthen support for a smooth transition so that we could have more leverage,'' Cai says. ''Of course, we will not interfere its domestic affairs. Thus the bilateral relationship will become better, unlike during the Kim Jong-il period when an issue is presented to China unexpectedly and without notice in advance.''

Already that policy is evident on North Korea's frozen land border, say activists who help North Korean refugees escape to South Korea by way of an underground ''railway'' through China.

''In the last year to 18 months the North Korean and the Chinese governments have been co-operating at a higher bureaucratic level to lock down the border, in anticipation of any developments like we have just seen with the sudden death of Kim Jong-il, to try to prevent any uncontrolled surge of people across the border,'' says Tim Peters, of a group called Helping Hands Korea in Seoul. ''We've seen a build-up of border patrols on both sides, and on the Chinese side the non-human element, the cameras and the heat and motion sensors.''

''There are still people escaping but the numbers are reduced,'' says the evangelical Durihana Mission's Chun Ki Won, who spent time in a Chinese jail after being caught trying to shepherd North Koreans into Mongolia during a blizzard. ''The exception are those organised by traffickers.''

The push factor of mass starvation in regions of North Korea and continuing harsh repression is worse than ever, say Peters and Chun. ''Nothing is relaxed, we don't see any reform going on, the economy is still moribund, agriculture is not improved, people are looking for the exit,'' Peters says. ''The lid is screwed tighter but the pressure in the cooker is building up.

''But that's very distinctly outside of Pyongyang. There are two North Koreas.'' One is Pyongyang with the sobbing mourners, and the other is outside the city, in the villages and towns - the outside world sees occasional pictures of them. ''These people haven't received public distribution [of food] for a long time - very little mourning [is] going on there.''

While Kim Jong-il made only half-hearted attempts at economic reforms, he did recently launch a modernisation drive aimed at making North Korea a ''strong and prosperous nation'' by the time of the 100th anniversary in April of Kim Il-sung's birth. The nuclear weapon has achieved the first goal, but brought down international sanctions that have hampered progress towards the second.

Still, the past year has seen the introduction of a mobile phone system by Egypt's Orascom with 900,000 subscribers already. The internet has spread to those with computers, a landline and electricity, though disconnected from the worldwide web. Students are being urged to study foreign languages and IT to help the country become a force in fields like data entry, programming and graphic animation.

''North Koreans don't have many distractions so they can study and reach perfection in what they do,'' Petrov says. ''I've met young Koreans speaking Russian with flawless accents, and who are very good computer programmers. The systems are cheap and efficient and don't interfere with the political regime.''

As well as securing the lion's share of available food, electricity, fuel and other resources, Pyongyang is increasingly sustained by deals, fees and bribes connected with Chinese trade. The uncle-regent Jang Song-taek is in the thick of this, says the dynastic chronicler Martin.

''He's bright, he's corrupt. He was sent away by Kim Jong-il for corruption on more than one occasion,'' Martin says. ''I have personally interviewed people who say he had cheated them in business deals. He's a guy who likes to make lots of money. There was a rumour, unconfirmed, a few years ago that he had offered to take over the economy and transform it in the way the Chinese have. But this didn't go over well with Kim Jong-il. This may have been one of the times he was sent away.''

Cai thinks that if nephew Kim Jong-un comes out on top, reform is unlikely. He had his fingers burnt last year with a mishandled currency revaluation, for which a senior official was shot as a public scapegoat. ''To carry out an economic test and fail is more dangerous in terms of politics [than doing nothing] and will threaten the regime's legitimacy,'' Cai says.

''Only when an opposition group brings down Kim Jong-un, will reform and opening-up become possible.''

Likewise, although the United States and North Korea were reported to be agreeing on a nuclear enrichment freeze in return for new food aid just as Kim died, few experts see Pyongyang giving up its nuclear deterrent. The attitude has probably stiffened since the fall of Libya's Muammar Gaddafi, since he had been cited by US negotiators as showing a dictatorship could give up its nuclear program without inviting Western intervention.

''They learnt a good lesson - a nuclear weapon is the only way to protect them and bargain with the West,'' Cai says. ''In fact, they don't even trust China and worry that China one day will betray [North Korea] as they see China is getting closer to United States. This will make de-nuclearisation even harder.''

North Korea's leadership transition has already fired up debate in South Korea, Japan and the United States about what policies can encourage reform and negotiation. Victor Cha, a national security official in the Bush administration, urges stepped-up preparation for North Korean regime collapse.

Michael Green, another Bush adviser, predicts an early nuclear test to show the new leader's resolve.

Wenran Jiang, a political science professor at the University of Alberta, counters that ''imminent collapse scenarios'' have consistently underrated the regime's survivability, notably for 17 years under Kim Jong-il in the most testing economic, human and strategic conditions.

''Contrary to Western media's portrayal of him as an erratic and somewhat unstable dictator with a funny hairdo who indulged in Hollywood movies, women and whisky, the older Kim was able repeatedly to put the United States and its allies in Seoul and Tokyo on the defensive, developed nuclear weapons under strict international sanctions and assured the regime's survival until today,'' Jiang wrote in the Toronto Star.

''On the few occasions when he was in the international spotlight, such as during meetings with former South Korean president Kim Dae-jung and Japanese prime minister Junichiro Koizumi, Kim Jong-il behaved in a rational, in-control manner, managing to extract the maximum from these high-profile negotiations.''

Jiang's advice for the West is to cool it, and keep at patient diplomacy. ''While it is absolutely necessary to co-ordinate and get ready for reckless moves from North Korea, the United States and its regional allies must tread carefully, refrain from calling for regime change and not entertain any thought of taking advantage of the succession to attempt a surgical removal of Pyongyang's nuclear arsenal,'' he says.

''It could be a dangerous miscalculation with catastrophic consequences.''

South Korea does not know what to do. Under its late president Kim Dae-jung in 1998-2003, it tried a ''Sunshine policy'' with Kim Jong-il, offering aid and investment in return for detente, but at high financial and moral cost it ended up with a nuclear-armed adversary.

The current conservative President, Lee Myung-bak, has taken a tougher line, drawing retaliation against South Korean projects and a string of serious military clashes, including last year's sinking of a South Korean warship and shelling of a small island community.

''So the Sunshine policy didn't work, but what's working now?'' says Donald Kirk, the author of Korea Betrayed, a book about the policy.

As the North goes into mourning and leadership consolidation next year, South Korea goes into its next political cycle with elections for its parliament in April and its new president in December.

Lee cannot run again for president, and his ruling party is almost certain to nominate Park Geun-hye as its candidate, with an excellent chance of being elected.

Park, 59, is the daughter of the fiercely anti-communist military dictator Park Chung-hee, assassinated by his intelligence chief in 1979. Her mother was assassinated earlier, by a pro-Northern ethnic Korean from Japan, and the daughter then acted as her father's political consort. Democracy also has its dynasties.

Korea has had its powerful women behind the throne - notably the Empress Myeongseong or ''Queen Min'', murdered by Japanese agents in 1895 - but no female ruler for more than 1100 years. In a year, the north's Great Successor might find himself up against a tough and unusual counterpart in the south.

With Sanghee Liu in BeijingAn insular peninsula

1392-1897: Under the isolationist Joseon Dynasty the Korean Peninsula is nicknamed the ''hermit kingdom''.

1910: Peninsula annexed by Japan after Russo-Japanese War.

1945: Peninsula divided into Soviet- and American-occupied zones after the end of World War II.

1948: Separate governments are established in both zones but the north refuses to take part in United Nations-run elections. Kim Il-sung becomes prime minister.

1950: Korean War begins after the governments of the north and south both claim sovereignty over entire peninsula. More than 2 million people die.

1953: Armistice ends fighting but no peace treaty signed and North Korea and South Korea still officially at war. A heavily guarded demilitarised zone on the 38th parallel still divides the peninsula.

1981: Oldest son Kim Jong-il designated heir apparent as ''Dear Leader''.

1994: Kim Il-sung dies. In death he is named ''Eternal President" in the North Korean constitution. He is succeeded by Kim Jong-il.

December 2011: Kim Jong-il, known variously as ''Dear Leader'', ''Generalissimo'' and ''Our Father'', dies. His third son, Kim Jong-un, is dubbed the "Great Successor" days after his father's death.