William and Harry at Pippa Middleton wedding
Prince William, Duke of Cambridge and Prince Harry arrive for the wedding ceremony of Pippa Middleton to James Matthews at St Mark's Church on 20 MayArthur Edwards - WPA Pool/Getty Images

Princes William and Harry are to pay tribute to their mother, Diana, a day before the 20th anniversary of her death with a visit to memorial garden dedicated to her at Kensington Palace.

The Palace said that the princes would visit The Sunken Garden on the palace's ground, which has been transformed in The White Garden in dedication to their mother. While there, the princes, accompanied by Kate, the Duchess of Cambridge, will meet with representatives of the many charities Diana supported during her lifetime.

Lady Diana's sons will also tour the gardens with the Head Gardener and another gardener who knew Diana from her visits, the palace said. The gardeners will discuss the area's design and planning and point out the princess's favourite plants.

According to a report in the Sunday Times, the princes will not be in public on the anniversary of their mother's death, and will stay at Balmoral. The Scottish castle was the place when the young princes were told of their mother's death by their father, Prince Charles,

Thursday 31 August marks 20 years since Diana, Princess of Wales, died from injuries sustained in a late night car crash in Paris.

She and her lover Dodi al Fayed were killed when the Mercedes they were travelling in crashed into a pillar in The Place de l'Alma underpass, Paris, while travelling at around 105 km/h (65 mph).

The tragedy prompted an unprecedented outpouring of grief in the UK while the Royal Family were criticised for their initial response

To mark the anniversary Wolf Hall author, Hilary Mantel described Diana as a princess "invented to fill a vacancy" in the public mind. "By her own account, Diana was not clever. Nor was she especially good, in the sense of having a dependable inclination to virtue", Mantel wrote in the Guardian, adding: "This is not a criticism."

It's not the first time Mantel has garnered nation-wide interest for her writing on princesses. The author drew the ire of royalists in 2013 when she described Kate Middleton, the Duchess of Cambridge and wife of Prince William, as appearing as if she was "designed by a committee and built by craftsmen, with a perfect plastic smile" in an LRB lecture.

"Presumably Kate was designed to breed in some manners," Mantel wrote.

It comes as a leading barrister has called for a new investigation into the death of Princess Diana, which he insists was not an accident. Michael Mansfield QC made the remarks ahead of the 20th anniversary of the Princess of Wales's death in Paris.

Mansfield is adamant that police did not properly investigate a note written by Lady Di before her death in which she claimed that her ex-husband Prince Charles was planning her death in a road accident.

Mansfield, who represented the Bloody Sunday families and the Guilford Four, made his comments to a US documentary exploring alternative theories about Diana's death, The Sun reported.

He said: "If you find a body at the bottom of the cliffs in Dover and the person has left a note saying, 'I'm going to end up at the bottom of the cliffs, dead' and, in the note, she'd indicated who she thought would be responsible for her death, I think the first port of call is to say, 'Hmm, well there may be something in this'."