Royal officials announced that the princes – along with William’s wife, Kate and their two children Prince George and Princess Charlotte- will attend the service, conducted by the Archbishop of Canterbury Justin Welby, in the grounds of Althorp House in Northamptonshire, on an island in a lake known as The Oval.
They will also be joined by members of Diana’s family at the event, which media are forbidden from attending.
It also emerged that Prince Charles will not be attending, as he and his second wife Camilla will be in Canada on the final day of a three-day tour.
William and Harry have also commissioned a statue of Diana to be erected in the future in Kensington Gardens and have supported a year-long programme of events for the Diana Award, a charity established to promote the princess’s belief in the power of young people to change society for the better.
The new commemoration comes just less than two months before the 20th anniversary of Diana’s death in a Paris car crash on August 311997.