The queen, who was admitted to hospital in October and regularly uses a walking stick, will not be attending next week’s Commonwealth Service at Westminster Abbey.
Prince Harry, who now lives in California, announced he would not be crossing the Atlantic for a memorial service for the Duke of Edinburgh, his grandfather, who died last year.
A representative for the Duke of Sussex declined to comment on the reason for his decision.
Prince Harry has pursued a legal challenge against the Home Office after being told he would no longer be given the “same degree” of personal protective security when visiting from the US, despite offering to pay for it himself.
He was last in London in summer 2021, when it is understood his security was compromised after his car was chased by paparazzi as he left a charity event.
The duke says he wants to bring his son, Archie, and baby daughter, Lilibet, to visit, but fears they are “unable to return to his home” because it is too dangerous, a legal representative previously said.
The queen’s decision not to attend Monday’s service was not related to any illness, but linked to discussions about the comfort of bringing the queen to and from the service.
The monarch, who celebrates her platinum jubilee this year, also suffered a bout of Covid-19 but has been doing light duties from home in Windsor Castle, west of London.
Prince Charles will act in her place at the annual service for the Commonwealth of 54 nations which she heads.
“After discussing the arrangements with the Royal Household, the queen has asked the Prince of Wales to represent Her Majesty at the Commonwealth Service at Westminster Abbey on Monday,” the Palace said in a statement.
“The queen will continue with other planned engagements, including in person audiences, in the week ahead.”
When the Duke of Edinburgh, the queen’s husband, died in April 2021 at age 99, Prince Harry flew back from California without the Duchess of Sussex, who was heavily pregnant at the time, to attend the duke's funeral in St George's Chapel, Windsor Castle.
The service of thanksgiving for the duke in a little more than two weeks' time is a chance for family, friends, dignitaries and representatives of the charities and organisations with which he was associated to gather together in tribute to him.