Singer Phil Collins claims to have witnessed Princess Diana's affair with James Hewitt first-hand.
The former Genesis drummer and frontman revealed in his memoirs how he saw the former lovers together in a car in London in 1991.
He even spoke to the Princess briefly and said she told him she had 'just had a colonoscopy' and recommended he "try it".
Collins, 65, has released a new book, Not Dead Yet, in which he reflects on his dealings with the Royal Family, whom he met through working with the Prince's Trust charity.
On the meeting with Diana, Collins said he was on the way to visit his dentist in Harley Street, Marylebone, with assistant Danny Gillen when he saw the couple.
He wrote: "A BMW pulls up and the window slides down. It's Diana and, sitting in the driver's seat, an officer-class chap I recognised as James Hewitt."
After a quick conversation about what he was doing in the area, Collins said Diana mentioned her medical procedure.
He added: "Light as you like, [she said] 'I've just had a colonoscopy. It was great. You should try it.' Danny and I look at each other. 'Did that really just happen?'"
Princess Diana first met Hewitt in 1986 when she hired the cavalry officer to teach her to ride in an effort to overcome a lifelong fear of horses.
They became friends and went on to embark on a five-year relationship while Prince Charles also had an affair with now-wife Camilla Parker Bowles, Duchess of Cornwall.
Hewitt, a tank commander for the British Army in the first Gulf , has had a spectacular demise over the past two decades, after he sold the story of his five-year affair with Diana.
In a move which was universally condemned, the former Gulf War hero drip fed intimate details of the pair's illicit relationship - yet maintained that he would never betray her.
Nearly two decades on and Hewitt is virtually broke, having lost two of his businesses, including a bar in Marbella, Spain, and a golf driving range.
He has also been reduced to sheltering under his elderly widowed mother Shirley's roof in a two-bedroom flat near Exeter.
Brazen Hewitt has never been shy about chasing the money and earned around £100,000 from Princess In Love, a book based on the pair's affair.
For a time, he made money from his memoirs and TV appearances, but the public appetite for details of the tawdry affair soon waned.
In 1993, he went on US television and declared he would sell the entire collection for £10 million.
But last year, in a sign of the depths to which he is willing to plumb, Hewitt tried to sell Diana's letters - notes which revealed their relationship - for a mere £100,000 (NZ$169,000).