REPORT: British princes discuss their mother Diana in new documentary

Britain's Prince William and Harry talk about the last phone call they ever had with their mother, Princess Diana, before she died, in a new documentary.

"Diana, Our Mother: Her Life and Legacy" is being released to coincide with the 20th anniversary of Diana's death in a Paris car crash on Aug 31, 1997.

"I think you get the private Diana," Nick Kent, the film's executive producer, told Reuters. "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 such aspect of Diana's life as her charity work involving HIV and landmines, it shies away from more controversial 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, 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.

"Diana, Our Mother: Her Life and Legacy" will be broadcast on British and U.S. television on July 24th.