Queen Elizabeth's eight grandchildren, including Princes William and Harry, will stand vigil beside her coffin for 15 minutes on Saturday evening, a Kensington Palace spokesman said on Friday.
Elizabeth's coffin will lie in state at Westminster Hall in London until Monday to allow members of the public to pay their respects to the late monarch.
"The Prince of Wales will stand at the Head, the Duke of Sussex at the Foot," the spokesman said, using William and Harry's royal titles. "At the King's request, they will both be in uniform."
Both William, the heir to the British throne, and Harry have served several years in the armed forces.
However, Harry, a veteran of the Afghanistan conflict, has not been permitted to wear military uniform at events so far as he lost his honorary military titles when he stepped down from royal duties in 2020.
Their spouses will not attend the vigil, the spokesman said.
(Reporting by William James, writing by Sachin Ravikumar and Angus MacSwan)