Prince William and Harry regret final words with Diana

Britain's Prince William and Harry have spoken of their regret over the last conversation they had with their mother Princess Diana before she died, saying the telephone call was "desperately rushed".

In a documentary called Diana, Our Mother: Her Life and Legacy, which screens in New Zealand on Three this week, the two princes said they spoke to their mother shortly before she died.

"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 says in the film.

"It was her speaking from Paris, I can't really necessarily remember what I said but all I do remember is probably regretting for the rest of my life how short the phone call was," adds Prince Harry.

Nick Kent, the film's executive producer, told Reuters he believed the documentary offered a glimpse of "the private Diana".

"Nobody has ever told this story from the point of view of the two people who knew her better than anyone else, and loved her the most: her sons."

The princes recall their mother's sense of humour, with Prince Harry describing her as "one of the naughtiest parents". They also recall the pain of their parents' divorce and how they dealt with the news of her death and its aftermath.

While the film addresses aspects of Diana's life such as her charity work involving HIV and landmines, it shies away from some other issues, such as extra-marital affairs.

According to the makers, however, the British 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, Prince 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.

A number of commemorative events have been planned to mark the 20th anniversary of Diana's death in a Paris car crash on August 31, 1997.

Diana, Our Mother: Her Life and Legacy will be broadcast on Three on Tuesday, July 25 at 8:35pm.

Reuters/Newshub