Ferrari Press Agency Ref 8208 Diana1 08/07/2017 See Ferrari text Picture MUST credit : ITV1 Young British royals Prince William and Prince Harry talk about their later mother Diana together for the first time in a documentary commemorating the 20th anniversary of her death.A trailer for Diana, Our Mother: Her Life and Legacy shows both of the princes leafing through a family album of photographs.The documentary, which is due to air on ITV in Britain and on HBO in the US later this month, will explore the relationship between Princess Diana and her two sons.Speaking in the film, Harry said: “This is the first time that the two of us have ever spoken about her as a mother.She was one of the naughtiest parents. 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.”The trailer shows the brother leafing through a family photo album./One snap shows Diana holding William whilst pregnant with Harry.William says: “Believe it or not, you and I are both in this photograph, you're in the tummy.”In April,Harry ,32, revealed how William encouraged him to seek counselling after two years of 'total chaos' as he struggled to come to terms with his mother's death.William ,35, implored his younger brother to get help after 'shutting down all his emotions' for nearly 20 years following Diana's death in 1997.Harry , who was 12 years old when his mother died, admits he ignored his grief during his teenage years, only addressing it when he was “on the verge of punching someone” in later life.efore that point, he endured two years of 'total chaos' when he became 'a problem' to himself - a period which included the infamous Nazi fancy dress and intimate photographs from a party in Las Vegas - but 'did not know what was wrong'. Diana died in a car crash on August 31, 1997 with her boyfriend Dodi Fayed when it smashed into a pillar inside Pariis tunnel in the early hours.An ITV spokeswoman 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.”Executive producer Nick Kent added: '”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.” OPS: William and Harry talking together and alone about their mother Diana in a clip from the trailer.Here they study the photo which was taken with Diana holding William while pregnant with Harry Picture supplied by Ferrari, Image: 341262699, License: Rights-managed, Restrictions: , Model Release: no, Credit line: Profimedia, Ferrari