Prince William, Prince Harry and Family Rededicate Princess Diana's Grave on Her Birthday

Event was held on what would have been the 56th birthday of the Princess of Wales, who died in a car crash in Paris in August 1997 at age 36

Prince Harry, Prince William and his family attended a private service Saturday to rededicate the grave of their mother, Princess Diana, on what would have been her 56th birthday.

The event was held two months before the 20th anniversary of her death. Williams' wife Kate Middleton, aka Catherine, Duchess of Cambridge, and their children Prince George, 3, and Princess Charlotte, 1, also attended, BBC News reported.

The service took place at Althorp House, Diana's family's estate in Northamptonshire in England. The princess's final resting place is on a small island on the estate's grounds. The area had recently undergone major renovations.

Diana's ex-husband and William and Harry's father Prince Charles did not attend the service. He is on a royal trip to Canada with his wife Camilla, Duchess of Cornwall, for Canada's 150th birthday.

Diana died in a car crash in Paris in August 1997 at age 36, with her boyfriend and driver. William was 15 and Harry was 12 at the time of her death.

In a new documentary, The Story of Diana, the princess' brother Earl Spencer reflects on her legacy. Diana was loved internationally and praised for her charity work.

"One of the reasons I want to talk now is because I think that after 20 years someone shifts from becoming a contemporary person, to one of history," he says in the film, which will air on ABC in two parts in August.

"And Diana deserves a place in history," he added. "This was a special person, and not just a beautiful one." 

Kensington Palace announced in January that a statue of Princess Diana will be erected on the grounds of the palace, her sons' home and her former home, at their request.

"It has been 20 years since our mother's death and the time is right to recognize her positive impact in the U.K. and around the world with a permanent statue," William and Harry said in a statement at the time. "Our mother touched so many lives. We hope the statue will help all those who visit when it will be unveiled. It is hoped that this will occur before the end of 2017."