'We let her down' Princes William and Harry open up about their mother's death ahead of BBC Diana documentary

Prince William and Price Harry are to appear in a new documentary about Princess Diana's death, saying they 'owe it' to their mother to honour her name 20 years after her fatal car accident.

In the new BBC documentary, which focuses on the week after Diana's death, both of Diana's sons will speak candidly about how they feel about losing their mother two decades later.

Speaking about why he became involved with the documentary, the Duke of Cambridge expressed feelings of letting his mother down and seeing this as a way to 'stand up' for her name.

'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.'

The documentary has been provisionally given the simple title of 'Diana' and will air in one 90 minute episode on BBC One this summer.

The programme will show the week following Diana's tragic passing from the perspective of her family, featuring exclusive interviews with both princes.

Prince Harry also commented on that heartbreaking time, recognising the 'huge effect' his mother had on the world.

'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.'

The 32-year-old prince continued to reflect on how difficult he finds the subject of his mother, but that the 20th anniversary of her death seems like the right time to 'to remind people of the difference that she made'.

'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.'