Prince William and Prince Harry open up about about the days following Princess Diana's death

In a heartbreaking new documentary, the brothers explain for the first time: "We let her down when we were younger. We couldn't protect her."

Prince William and Prince Harry will talk in detail for the first time about the days and weeks following the death of their mother in a new BBC documentary.
William was just 15 and Harry only 12, when their beloved mother, Diana, Princess of Wales, was tragically killed in a car crash in Paris on 31 August 1997.
She was just 36.
In a teaser for the feature-length documentary, provisionally called Diana, the Duke of Cambridge, 34, explains he and his younger brother felt compelled to comment or “stand up” and protect their mother -- something they weren’t able to do at the time of her tragic passing.
"Part of the reason why Harry and I want to do this is because we feel we owe it to her," William said. "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 boys were just 15 and 12 respectively when their mother died in a car crash.
Since her tragic death in 1997, William and Harry have made it their life’s work to continue their late mother's incredible legacy.
Prince Harry, 32, added: "When she died there was such an outpouring of emotion and love which was quite, which was quite 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."
The 90-minute feature, one of two authorised documentaries about the ‘People's Princess’ that will be released this year to mark the 20th anniversary of her death, will also include interviews with close friends, political figures and journalists.
Air dates for the documentary are yet to be announced.
WATCH: A candid Diana charms the crowds. Post continues...
Harry recently revealed he didn't deal with the grief of losing his mother until decades later, which ultimately lead to a myriad of mental health issues.
In a raw new interview with the UK's The Telegraph, he said it wasn't until the age of 28 that he addressed it.
The 32-year-old told Bryony Gordon for her Mad World podcast that he was “very close to a complete breakdown on numerous occasions” and living in the public eye only exasperated his anxiety.
“I can safely say that losing my mum at the age of 12, and therefore shutting down all of my emotions for the last 20 years, has had a quite serious effect on not only my personal life but my work as well,” he explained.
“I have probably been very close to a complete breakdown on numerous occasions when all sorts of grief and sort of lies and misconceptions and everything are coming to you from every angle.”
Harry admits he didn't deal with Diana's death until his late twenties.
When questioned if he had seen a "shrink" for help, the Prince revealed: “I’ve done that a couple of times, more than a couple of times, but it’s great.”
Before getting help, the royal admits to conning himself into thinking he was OK.
“So I was a typical 20, 25, 28-year-old running around going ‘life is great’, or ‘life is fine’ and that was exactly it," he said.
WATCH: Prince Harry speaks about his desire to honour his late mother's life. Post continues...
“And then [I] started to have a few conversations and actually all of a sudden, all of this grief that I have never processed started to come to the 
forefront and I was like, there is actually a lot of stuff here that I need to deal with.”
He said it was “only two years … of total chaos” before he was comfortable to express his feelings.
“I just couldn’t put my finger on it. I just didn’t know what was wrong with me.”
Thankfully, Harry said seeking help has left him in a "good place."