Prince George and Princess Charlotte will be page boy and bridesmaid when their aunt Pippa Middleton gets married in May.
"Miss Pippa Middleton and Mr James Matthews are pleased to confirm their wedding will take place at St Mark's Church, Englefield, on the morning of 20th May," a statement said.
It went on to confirm that Pippa's niece and nephew will play key roles in the ceremony.
Unusually the announcement from Pippa and her fiancé came via a press release from Kensington Palace.
It was also confirmed that the Duke and Duchess of Cambridge and Prince Harry will be among the guests, with the service attended by close family and friends.
There has been growing speculation among royal watchers about whether the younger royals would be involved in the wedding, especially as Prince William and Kate are hugely protective of their children's privacy, and would be conscious of upstaging Pippa on her big day.
Many had also wondered whether Kate would be her sister's matron of honour.
James Matthews, who is a hedge fund manager, proposed in July 2016 while the couple were in the Lake District.
During the royal wedding in 2011, Pippa found herself at the centre of media attention after wearing a figure-hugging Alexander McQueen bridesmaid dress to follow her sister Kate down the aisle of Westminster Abbey.