Hasnat Khan has never been one to follow his own advice. As a heart surgeon he tells his patients to stay away from greasy foods, do lots of exercise and keep healthy. As an individual he eats takeaways, smokes heavily and drinks a lot of coffee. Those who know him say he is a quiet, shy man who likes to keep himself to himself. In 1995 he started dating the most famous, least private individual in the world - the Princess of Wales.
But while Diana's ill-fated escape from the long lens and tabloid obsession has at least saved her from the pain of further intrusion, Khan has lived on as one of the few remaining people in her life around whom some mystery remained.
Until now, at least. For just when we thought there could not possibly be anything more to reveal, yet another branch of the Diana memorial industry has emerged with news that Hasnat was not just the man she loved, but the man she intended to marry.
In a documentary tonight, Imran Khan (no relation) will confess that the princess asked him to act as a marriage broker between her and Hasnat. "It was clear she was very deeply in love with him," says the cricketer-turned-politician. "I don't think she could have got over it that quickly." His confession comes hot on the heels of another book, Diana: Her Last Love, by Kate Snell, which is dedicated solely to the affair.
Khan is as unlikely a candidate for tabloid fodder as he was as a partner for Diana. He is neither indiscreet nor of aristocratic stock, like James Hewitt; nor is he a flashy playboy type like the late Dodi Fayed. He is a chubby-faced, unimposing, moustachioed doctor dedicated to his work.
True, he has been compared to Omar Sharif and described as the "dishy doctor", and, after she broke up with Prince Charles, Diana vowed she would never again become involved with an Englishman. But place him in a lineup of probable mates for the late princess and it is doubtful that he would be picked out.
Nor is there much in his background to suggest that he would find himself in such a situation. Contrary to reports about his humble beginnings, he was raised in a wealthy, middle-class family in Pakistan, near the city of Jhelum, about 120 miles north of Lahore.
He was the eldest child in a family of four. His father, Rasheed, helped to found a successful business making glassware and bottles for the domestic market. But the real head of the household was his grandmother, Mrs Forkhunda Ayyub, known as Nanny Appa, a fact that would be of vital importance as his relationship with Diana developed. Hasnat attended and excelled at a Convent school in Jhelum, which he left to study medicine in Lahore after his A-levels. When his studies were over he went to Australia, where he started to specialise in heart surgery thanks to his uncle's contacts. He finally settled in England in the early 90s.
By all accounts his first meeting with Diana did far more for her than it did for him. He was working in the Royal Brompton heart and lung hospital, assisting in a triple heart bypass operation that was being performed on Joseph Toffolo, the husband of Diana's acupuncturist, Oonagh.
Diana had just arrived to see Joseph when Hasnat walked in. "He merely acknowledged her with a formal nod then proceeded to focus on Joseph's condition," Oonagh told Snell. "It is doubtful whether the Princess of Wales had ever made less of an impression on anyone in her entire life." Hasnat rather incredibly claims that at the time he had no idea who she was. "I didn't even recognise her," he says.
But as her visits to the hospital became far more frequent they got to know each other well. When she was spotted making a late night visit to the Brompton one winter's evening by a News of the World photographer, she called the paper's Royal editor on his mobile and told him she was simply there to comfort the sick and dying.
The knowledge that the media were on to something did not temper her ardour. Indulging Hasnat's love of jazz, she bought him CDs of Ella Fitzgerald, Louis Armstrong and Dave Brubeck, and accompanied him to Ronnie Scott's jazz club in Soho.
But even though the affection was not exactly one way, Diana had invested far more in the relationship than Hasnat did. He had never been lucky in love. He was engaged to a Pakistani doctor, Nazra Nasim, for three years before she married somebody else. And his second fiancee, Furial Anwar, called off their relationship after a year. Diana wanted to run away with him to Australia or South Africa where she thought they could "be alone".
During a visit to Pakistan in 1997 Diana slipped away from the media pack to visit his family in Jhelum. Whatever Hasnat's feelings, there could be no marriage without the consent of Nanny Appa, and while the subject was not broached directly Diana felt she should meet his family.
A year earlier she had entertained Nanny Appa at Kensington Palace, where Diana presented her with a silver rose bowl. A video of the meeting shows Diana's relief as Hasnat's grandmother touched the princess's cheek in gratitude. At one point, Mrs Ayyub, a Muslim, lifted up the corners of her sandwiches, apparently checking to see if they contain ham. Diana assured her the filling was salmon.
But within a year Hasnat's affections had cooled. He was fond of the princess but could not handle the media scrums and intrusive reporting. It was around this time that she sought the help and counsel of Imran Khan. "I was going to talk to him to find out the reason," he says. "Having married someone from outside my culture, if there was something that could be cleared up, or some advice given, maybe I could help." This is why he believes that the pictures of the princess's final days with Dodi Fayed were deliberately calculated to make Hasnat jealous and win him back.
Diana: Her True Love, Channel 5, tonight 8pm