Premiering on July 24, the new authorized documentary Diana, Our Mother: Her Life and Legacy celebrates the life and work of Diana, Princess of Wales, in the 20th year since her tragic death.

The film features intimate interviews with HRH The Duke of Cambridge and HRH Prince Harry, who speak openly about their mother and pay tribute to the many ways her influence has shaped them. The film also pays tribute to Princess Diana’s philanthropic legacy, and the how that has played a role in both of their public lives.

In this trailer, William and Harry are looking through a photo album put together by their mother. This is the first time the two brothers have ever spoken about her as a mother. “She was very informal and really enjoyed laughter and the fun,” William says. “She was one of the naughtiest parents,” recalls Harry. “She was our mum. She still is our mum. And of course, as a son I would say this, she was the best mum in the world. She smothered us with love, that’s for sure.”

In addition to William and Harry’s contributions, the documentary also includes interviews with many key figures in the Princess’ life and new archival footage. According to Nick Kent, the film’s executive producer “This film shows Princess Diana in a way she has never been seen before, through the eyes of the two people who knew her best.”

Diana, Our Mother: Her Life and Legacy premieres July, 24th on HBO and on demand July 25th