Prince William and Prince Harry are set to talk about the immediate aftermath of their mother Diana's death in a new BBC documentary as they feel they "owe it to her".

As the 20th anniversary of their mother's death takes place in August, the royals will discuss the week that followed her passing in a special film, provisionally called Diana.

The documentary features in-depth interviews with her sons in which they speak in detail about that week's events, from hearing the news of her death to the day of her funeral.

In the documentary, Prince William said: "Part of the reason why Harry and I want to do this is because we feel we owe it to her.

"I think an element of it is feeling like we let her down when we were younger. We couldn't protect her.

"We feel we at least owe her 20 years on to stand up for her name and remind everybody of the character and person that she was. Do our duties as sons in protecting her."

Prince William and Harry feel they couldn't protect mum Diana

Prince Harry said: "When she died, there was such an outpour of emotion and love which was quite... which was shocking.

"It was beautiful at the same time, and it was amazing, now looking back at it, it was amazing that our mother had such a huge effect on so many people.

"When you're that young and something like that happens to you, I think it's lodged in here, there, wherever - in your heart, in your head and it stays there for a very, very long time.

"I think it's never going to be easy for the two of us to talk about our mother, but 20 years on seems like a good time to remind people of the difference that she made not just to the royal family but also to the world."

Princess Diana's sons want to honour her memory in new documentary

Friends and family of the royals, as well as political figures and journalists, will feature in the 90-minute BBC film, many of them speaking for the first time about the events of that week in August 1997.

Prince Harry recently opened up about grief and experiencing two years of "total chaos" following the death of his mother Princess Diana in a bid to break the stigma surrounding mental health issues.