In the two-hour film, William, 35, and Harry, 32, share their initial reactions to finding out that Diana died in a car crash in Paris at the age of 36 in August 1997. They also open up about their mother's funeral and the outpouring of support they received from fans worldwide.
"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 says. "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 everyone of the character and person that she was, do our duties as sons in protecting her."
In the trailer, Harry recalls mourning with the massive crowds that gathered after the news. "I remember people's hands were wet because of the tears that they just wiped away," he says.
"When she died there was such an outpour of emotion and love, which was quite shocking," Harry says in the special. "It was beautiful at the same time, and it was amazing now looking back at it. I think that our mother had such a huge effect on so many people."
The documentary is one of the many airing in honor of the upcoming 20th anniversary of the Princess of Wales' death. "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," Harry says in the film.
Diana, 7 Days airs on NBC on Friday, September 1, at 8 p.m. ET.
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