James Hewitt, a former army officer who served in the Queen's Life Guard regiment, was romantically linked with Diana for five years during the late 1980s before he was called up to serve in the first Gulf War. The pair met at Buckingham Palace and, in 1986, he was employed to conduct her horse riding lessons.

On Sunday, the 58-year-old appeared on Channel Seven's Sunday Night in a feature commemorating 20 years since her death.

As well as her affair with Hewitt, the hour-long special canvassed her struggles with bulimia, her admirers - including a US politician who promised to make her First Lady - and how, after seeking counsel from psychics, she believed Prince Charles was plotting her death.

Host Melissa Doyle, who travelled to the United Kingdom for the interview, didn't pull any punches.

"Are you Harry's father?" she asked an emotional Hewitt.

"No I'm not," he said.

"Why does that keep being repeated?" Doyle asked.

"It sells papers," he said.

"That's heartbreaking for you and him."

"It's worse for him probably. Poor chap," Hewitt said, staring down the barrel of the camera.

Hewitt, who never married or had children, also spoke of how they enjoyed secret meetings together which involved a lot of "frivolity, escapism, walking, laughter and cooking. Me cooking and her washing up," he said.

Hewitt was joined by Diana's former butler, Paul Burrell, her bodyguard Ken Wharfe and best friend Rosa Monckton in what Seven was touting as a "royal event".

All four are no strangers to the spotlight since her death in 1997. They each have cosy relationships with the press and have capitalised, in a variety of ways, on their relationships with her in the past.

Hewitt especially, who is now reportedly broke and living with his widowed mother in a small cottage in Devon.

He once boasted on US television he was offered more than $16 million for a cache of letters from Diana and two he received from a five-year-old Prince William.

In 2015 it was reported he was prepared to sell them for little more than $150,000.

A spokeswoman for Seven wouldn't comment if he or others involved in the program were paid by the network to participate.

"We don't discuss arrangements with any of the people we interview on Sunday Night," she told Fairfax Media.