Prince William and Harry felt they "couldn't protect" their late mother Princess Diana when they were younger.

Prince William and Prince Harry

Prince William and Prince Harry

The royal brothers tragically lost their parent in a car crash in Paris, France, in 1997, and have revealed the reason they decided to make a 90-minute long BBC documentary about Diana, which has yet to be named, is because they feel they "owe it to her" to prevent her name from being tainted now they are older as they feel they "let her down" when they were children.

Speaking in a clip of the programme, the Duke of Cambridge 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.

"Do our duties as sons in protecting her."

William and Harry hope the tell-all programme will "remind everybody" of Diana's true character, especially after the recent drama titled 'King Charles III' controversial plot depicted their father Charles, the Prince of Wales - who was married to Diana for 15 years until 1996 - in a negative light as he plotted to overthrow the monarch in the programme.

William said: "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."

The programme will not only explore William, 34, and his 32-year-old brother's recollection of their mother, but it will also include interviews with those who were close friends of Diana's as well as political figures.