Kensington Palace, where the intimate event is being held, has confirmed the slimmed-down guest list.

There was no mention of the Duchesses of Cambridge or Sussex, as Harry and William look set to be the only senior royals in attendance.

Kate’s absence will deprive the brothers of a unifying figure at the occasion after their once close relationship came under unprecedented strain in recent months.

In March, Harry told Oprah how he felt sorry for William and his dad Prince Charles, who he described as being ‘trapped’ within the system of the monarchy.

The brothers last met in person in April at the funeral of grandfather Prince Philip – and the author of a book on the duo has said there was a furious row between them shortly afterwards.

The bust-up was revealed by historian Robert Lacey, author of Battle Of Brothers: William, Harry and the Inside Story of a Family in Tumult.

The Daily Mail reports that Kate attempted to act as a peacemaker, talking to Harry as they walked out of St George’s Chapel.

Diana’s statue will be unveiled on Thursday in the Sunken Gardens in Kensington Palace

Prince William and Harry will be the only senior royals at the event

But within minutes, the princes were quarrelling again, according to Lacey. A source told him: ‘There they were – at each other’s throats as fiercely as ever.

‘The rage and anger between these two has grown so incredibly deep. Too many harsh and wounding things have been said.’

Despite the conflict, the brothers will attempt to put their differences aside and commemorate Diana’s life and legacy, on what would have been her 60th birthday.

Announcing the guest list, Kensington Palace said: ‘Prince William and Prince Harry will attend a small event to mark the unveiling of a statue they commissioned of their mother, Diana, Princess of Wales, in the Sunken Garden at Kensington Palace on Thursday, July 1.

Operational note from Kensington Palace Diana about the statue uneviling event

Prince Harry flew home to the UK on Thursday

‘In addition to close family of Diana, Princess of Wales, members of the statue committee, the sculptor Ian Rank-Broadley, and garden designer, Pip Morrison, will also be present.’

Harry and William commissioned the artwork in 2017 – the 20th anniversary year of Diana’s death – to celebrate the princess with the creation of a permanent statue.

They said in a statement when the project was announced: ‘Our mother touched so many lives. We hope the statue will help all those who visit Kensington Palace to reflect on her life and her legacy.’