Princes William and Harry are expected to spend the morning together remembering their mother on the 22nd anniversary of her death.
The boys were just 15 and 12 respectively when Diana, Princess of Wales, was killed aged 36 in a Paris car crash.
The brothers always come together to support each other on the sad anniversary.
The pair use the opportunity to look through old photographs and talk about their favourite memories, according to Hello magazine.
They will spend the morning alone before being joined by Kate and Meghan and their children in the afternoon.
It will be the first time that Princess Diana’s fourth grandchild, Archie, will join the occasion.
A source told the magazine: ‘They talk about the little things about Diana that made them laugh: the ski trips and outings to Thorpe Park; the effort she went to on their birthdays – all of it.
‘Their other halves and kids join them later.’
Fans of the Princess, who died after an accident in a Paris underpass on August 31, 1997, are expected to gather at Kensington Palace.
On what would have been her 58th birthday last month, Prince William stunned fans with a walkabout outside his late mother’s former home, which is also where he now lives.
The Duke of Cambridge and his brother, the Duke of Sussex, spoke candidly and often about their mother in the run-up to the 20th anniversary of her death.
They both described the personal anguish they experienced and the grief they still feel.
And in the intervening two years, they have continued to speak about their mother, with Harry describing how she and wife Meghan would have been ‘thick as thieves’.
Prince Harry will also follow in her footsteps when he visits Angola in September to highlight the plight of landmine victims – a cause the princess championed in the months leading up to her death when she famously walked through a cleared Angolan minefield.
The crash that killed Diana also claimed the lives of her boyfriend Dodi Fayed and their driver Henri Paul.
William and Harry were both pupils at Eton when their mother was killed and they would later, with other senior royals, walk behind her funeral cortege.
The royal brothers have already planned their own permanent memorial to their mother.
Sculptor Ian Rank-Broadley was chosen by William and Harry to create a statue of Diana.
The design for the artwork has been chosen and will be erected in the grounds of Diana’s former home Kensington Palace.
Princess Diana ripped up the royal rulebook in taking a hands-on approach to raising her boys.
She shunned the tradition of letting nannies do most of the child-rearing and made a point of being very involved.
She was only 21 when she became a mum and she insisted on taking them on Royal Tours and being involved in school events.
It is an approach both her sons have continued with Princes William and Harry also limiting the number of nannies for their young children.