Image copyright PA Image caption The princes will attend a private service at their mother's grave, nearly 20 years after her death

The Duke and Duchess of Cambridge and Prince Harry are to attend a service to rededicate the grave of Diana, Princess of Wales, almost 20 years after her death.

The private service is at Althorp House in Northamptonshire on Saturday, which would have been her 56th birthday.

Prince George, Princess Charlotte, Princess Diana's brother, Earl Spencer, and her two sisters will also be there.

Prince Charles and the Duchess of Cornwall will be in Canada.

The service will be conducted by the Archbishop of Canterbury Justin Welby.

The Princess of Wales died on 31 August 1997 in a car crash in Paris, when the Duke of Cambridge was 15 and his brother was 12.

Image copyright PA Image caption Prince William with his mother, Diana, Princess of Wales, in 1994

The princes have commissioned a statue of Princess Diana to mark the 20th anniversary of her death.

The sculpture will be placed in the public grounds of her former residence, Kensington Palace.