In a deeply moving and emotional baring of a grief that will never fade, Princes William and Harry have revealed their regrets about the final conversation they had with Princess Diana.

The princes, who were 15 and 12 respectively when their mother died in a Paris car crash on August 31, 1997, told filmmakers their last conversation was a brief phone call with the holidaying princess because they wanted to return to playing with their cousins.

The brevity of that call, which came mere hours before she died, still troubles the young Royals.

“Harry and I were in a desperate rush to say ‘goodbye’, you know, ‘See you later’… If I’d known now, obviously, what was going to happen I wouldn’t have been so blasé about it and everything else,” Prince William said.

“But that phone call sticks in my mind, quite heavily.”

Princes Harry and William pick through an album of their mother’s memorabilia in a scene from the documentary.

Harry, 32, tells the filmmakers the brevity of that final chat is something he will regret until he dies.

“Looking back on it now, it’s incredibly hard,” he said. “I’ll have to sort of deal with that for the rest of my life.

“Not knowing that was the last time I was going to speak to my Mum. How differently that conversation would have panned out if I’d had even the slightest inkling her life was going to be taken that night.”

Excerpts of the ITV documentary Diana, Our Mother: Her Life and Legacy — which will air in Britain this week — and new family photographs were released today.

It is only in the last year that William and Harry have spoken in public of their feelings about the sudden loss of their mother.

The documentary chronicles Diana’s charitable works, including her historic outreach to AIDS victims and campaign to ban land mines.

The princes also stress their mother’s fun-loving side, which they say the public generally did not see.

“Our mother was a total kid through and through. When everybody says to me, ‘So she was fun, give us an example’, all I can hear is her laugh in my head,” Prince Harry said.

Prince William, second in line to the throne, tells a story that reveals the privileged life they led as children.

He said one day Diana surprised him by having three of the world’s top models waiting for him when he got home from school.

“She organised when I came home from school to have Cindy Crawford, Christy Turlington and Naomi Campbell waiting at the top of the stairs,” he recalled.

“I was probably a 12- or 13-year-old boy who had posters of them on his wall.

“I went bright red and didn’t know quite what to say. And sort of fumbled and I think pretty much fell down the stairs on the way up.”

Prince William, 35, said he frequently tells his children — Prince George, 4, and Princess Charlotte, 2 — about Diana so she can be a presence in her grandchildren’s lives.

“She’d be a lovely grandmother. She’d absolutely love it, she’d love the children to bits,” he said.

Princess Diana’s desk , recreated as she left it for the documentary.

Nick Kent, the film’s executive producer, said the Royals were very open, and did not put any subject off limits. Rather, they wanted to cover new ground and make a different type of film.

“What we had in mind is that in years to come, Princes William and Prince Harry would be happy to show this film to their own children and say this is who your grandmother was,” Kent said.

The program is one of a series of tributes to Diana expected as the 20th anniversary of her death approaches.

-AAP