Princess Diana’s life (and coverage of her death) largely played out in the eyes of a scrutinizing public. However, a new HBO documentary about the late royal is shining the spotlight on those who knew her best and giving them the last word on shaping her lasting legacy.

The subscription network announced Tuesday it will air a nonfiction feature recounting Lady Di’s impact as a humanitarian and mother, as told through interviews with her sons, Prince Harry and Prince William, Duke of Cambridge, whom “talk openly and in depth about their mother and how her influence has shaped their lives” in the film, according to a press release.

“This film will show Princess Diana in a way she has never been seen before, through the eyes of the two people who knew her best,” executive producer Nick Kent said via statement.

Nearly 20 years after Diana’s death in a car crash in September 1997, the project will additionally delve into her charity and philanthropic work, which included tackling issues relating to child welfare, homelessness, HIV, AIDs, and international initiatives to ban landmines.

Currently untitled, the film — directed by Ashley Gething and produced by Oxford Film and Television — is also set to feature contributions from friends and other members of Diana’s family, some of whom have never spoken publicly about her.