Princess Diana died 20 years ago this August, and the anniversary of her death is expected to be marked in a number of television tributes.
A documentary for ITV will feature relatives and those who knew her, including William and Harry's perspective on their mother's charitable and humanitarian work.
William was 15 and Harry just 12 when their mother was killed in a car crash in Paris on August 31, 1997.
Jo Clinton-Davis, controller of factual at ITV, who co-commissioned the programme, said: "This new ITV film will offer viewers a fresh and revealing insight into Princess Diana through the personal and intimate reflections of her two sons and of her friends and family, many of whom have never spoken before, to bring together a definitive portrait of a unique person who touched the lives of millions."
Areas including landmines, child bereavement, homelessness, HIV and Aids will be explored.
Nick Kent, the documentary's executive producer from Oxford Film and Television which is making the programme, said: "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."
ITV has said the film will be broadcast later in the year.