In fact, they were only replicas, on display in the Queen Victoria Building in Sydney, but Mr Coleman was hooked for life.

“I would sort of stand mesmerised by their beauty,” he said.

“They're nothing to the originals, but they really sparked an interest for me.”

Although he has never visited England – or even left Australia – the 23 year old has since become an expert on the British Royal Family, with a particular interest in the Queen's jewellery collection.

“The Queen has multitudes of really fabulous jewels, and I've always been interested in them because they've been a silent witness to great historic events, like royal weddings and coronations and revolutions,” he said.

“Many of them have gone through wars and have fantastic stories attached to specific diamonds and specific pieces that the Queen continues to wear today, so I've always been interested in that.”

He said he had built up his knowledge of royal history mostly through books and exhibitions, and was disappointed not to be able to fly to England in 2011 for the Royal Wedding due to health problems.

He did, however, manage to score an invite to Government House for the Queen's visit in 2011, and had the opportunity to “say hello” to the monarch.

He will be giving a lecture on Sunday at the National Portrait Gallery, focusing on the recent royal portrait by Sydney artist Ralph Heimans, in which Queen Elizabeth is wearing a particularly magnificent diamond necklace.

Mr Coleman will be explaining how the diamonds once belonged to Queen Victoria who, finding herself without a significant collection of jewellery upon being crowned Queen of England, set about rectifying the situation.

“She had a lot of useless bits and pieces that she couldn't wear, like a great jewelled sword and huge big badges of various orders of the garter and thistle,” he said.

“She had all these big, big diamonds prised out of old useless pieces and had them made into a beautiful necklace. That necklace is known now as Queen Victoria's coronation necklace, although it wasn't made until the 1850s, many years after her own coronation. It has been worn by every queen, consort and of course the monarch, ever since.”

He said it was difficult to imagine the size and splendour of the jewels in the portrait, which together comprise more than 100 carats.

“What I'll be talking about in detail is the way the jewels have been adapted to be worn by successive queens to suit their own tastes, and changing fashions of the day.”

The replicas that so captivated him in the 1980s were, in fact, made by Garrards of London, the royal jewellers famous for creating Princess Diana's engagement ring, and were commissioned for the re-opening of the Queen Victoria Building in 1985.

They've since been donated to the Museum of Australian Democracy at Old Parliament House in Canberra, and Mr Coleman will have several on hand as props for his talk.

He will also be discussing the Queen's personal collection, and her penchant for revisiting her favourite pieces and loaning items out to family members for important events.

Although he lives in Queanbeyan and has never had the opportunity to travel to London, he said he had always had a private passion for royal jewellery.

“My grandfather was a jeweller and my great-grandfather, and in our family we've always had a passion – a more modest passion than the Royal Family – but always had a passion for gems and jewellery, and specifically Australian jewels.”

This is at least one thing he shares with the Queen, who he said had a special fondness for the Australian jewels she had throughout her reign.

“One was a wattle brooch, a very beautiful wattle brooch made in Melbourne using yellow diamonds and Australian blue-white diamonds, which was presented to her in 1954 when she came to Australia, and Her Majesty has continued to wear it very regularly,” he said.

“It's one of her favourites, not only when she comes to Australia but for family events like the wedding of Prince Charles to the Duchess of Cornwall.”

He admitted that whenever he saw a photograph of the Queen, the first thing he checked was her jewellery, and was usually able to identify its provenance.

“It's always very interesting to see a piece that has resurfaced after many years of not being worn, or just being put in a safe somewhere,” he said.

“But I think the marvellous thing about Her Majesty's collection is that she continues to wear these pieces. They don't just languish.”

Scott Coleman will be giving a lecture on the Queen's diamonds at the National Portrait Gallery on Sunday February 10 at 2pm. Entry is free.