Princess Diana's sons William and Harry hope 'to make a difference' to honor her memory

Princes William and Harry are hoping to keep their mother's legacy alive by trying "to make a difference" through work that would have made Princess Diana proud. 

The princes appeared in the new documentary, "Diana, 7 Days" and revealed how they are trying to fill the void that was left 20 years ago when Diana died in a car crash in Paris. The princes were 15 and 12 years old at the time of their mother's death. 

"All I want to do is try and fill the holes my mother has left," Harry, 32, said in the documentary. "And between myself and William, and everybody else that's in those privileged positions, to try and make a difference. And that's what it's about for us, trying to make a difference." 

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William, 35, echoed that sentiment, saying he pushed through her tragic death by thinking about what he and Harry can do to make their mother proud. 

"Both our parents have brought us up to understand that...there is this element of duty and responsibility that you have to do things you don’t want to do," William said. 

He added, "When it becomes that personal, walking behind your mother’s funeral cortege, it goes to another level of duty. But I just kept thinking about what she would want and that she’d be proud of Harry and I. And effectively, she was there with us. It felt like she was walking alongside us to get us through it."

The documentary is set to premiere on Friday. 

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William and Harry have worked at several charities that were close to Diana's heart since she died. Diana was known for taking several causes including HIV/AIDS awareness, homelessness and mental health. She was linked to more than 100 organizations -- many of which her sons have also worked with to continue her work. 

Thursday marked the 20th anniversary of Diana's death. Harry and William, along with his wife Kate Middleton, Duchess of Cambridge, toured the memorial garden in Kensington Palace on Wednesday. Several celebrities, including Elton John and Piers Morgan, posted tributes on their social media page honoring the late princess.