According to the tagline on posters for the new biopic portraying Princess Diana’s love affair with a Pakistani heart surgeon, “the legend is never the whole story.”

Now the man at the centre of the narrative, Hasnat Khan, has spoken out to insist that the film itself does not tell the whole story either, being based entirely “on hypotheses and gossip.”

Dr Khan, who was nicknamed Mr Wonderful by the Princess, launched a scathing criticism of the forthcoming big budget release, Diana, claiming it was “completely wrong” and vowing he would never watch it.

A still image from the film showing the actors playing him and Diana side by side at the hospital where they met was enough to convince him it would entirely misrepresent their relationship, he said.

“I don’t see this movie doing well at all,” he said.

“It is based on gossip and Diana’s friends talking about a relationship that they didn’t know much about, and some of my relatives who didn’t know much about it either. It is all based on hypotheses and gossip.”

The film, due to be released in the UK next month, stars Naomi Watts as the late Princess and Naveen Andrews as the cardiologist who became her lover.

Directed by Oliver Hirschbiegel, it focuses on the final two years of Diana’s life and will be the first to cover in detail her death in a car crash in Paris in 1997.

But Dr Khan said the actors’ stance in the still, standing side by side, told him all he needed to know about how the film would portray things, and he could see it was “wrong.”

He told the Mail on Sunday: “I could tell immediately those were never our mannerisms at all, with [my] hands folded behind the back and all that.

“You could tell from that picture that it is all just presumed about how we would behave with each other, and they have got it completely wrong.

“There wasn’t any hierarchy in our relationship. She wasn’t a Princess and I wasn’t a doctor. We were friends, and normal people stand like friends with each other.”

He said the filmmaker and Kate Snell, who wrote the book on which the film is based, had approached him on a number of occasions, but he had refused to cooperate.

Jemima Khan, Diana’s close friend, said last month that the Princess had been “madly in love” with Dr Khan, with whom she had a two-year relationship.

Diana had wanted to marry the doctor and secretly met his family in Pakistan to discuss the possibility of a union, Mrs Khan told Vanity Fair.

The couple are thought to have discussed the possibility of marriage, but Dr Khan told police in an interview after Diana’s death in 1997 that he had said to her “it was a ridiculous idea” and that the only way they could have a normal life would be to move to Pakistan, where the press “don’t bother you”.

Diana began a new relationship with Dodi Al Fayed shortly before the end of her life, as her relationship with Dr Khan began to fall apart.

Another friend of Diana’s, Rosa Monckton, said the Princess talked much more about Dr Khan than Mr Al Fayed, adding that she still believed she only pursued the relationship with the latter to arouse the doctor’s jealousy.