Prince William and Prince Harry will talk in detail for the first time about the moment they found out about their mother's death in a BBC1 documentary to honour the late Princess Diana.
The brothers were 15 and 12 when Diana died in a car crash in Paris in 1997, and they speak candidly about the aftermath of the tragedy from their perspectives in the 90-minute film.
'Part of the reason why Harry and I want to do this is because we feel we owe it to her,' the Duke of Cambridge relays in a clip from the documentary, which was broadcast at a BBC reception last night (via ).
'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 Harry admitted that the outpouring of grief from the public was overwhelming, adding: '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.'
A BBC spokesperson said that the documentary is part of the broadcaster's new factual season, and will 'tell the inside story of the tumultuous and unprecedented week that followed the death of Diana, Princess of Wales, and explore how she came to have such an extraordinary effect on the nation and people around the world.'
Diana will air on BBC1 later this summer.