Queen Elizabeth II canceled a planned public appearance Sunday after spraining her back.
In a statement, Buckingham Palace said the queen "has decided this morning with great regret that she will not be able to attend today's Remembrance Sunday Service at the Cenotaph."
It said she was "disappointed that she will miss the service."
This is the first time the 95-year-old monarch has missed the Cenotaph because of ill health, ABC News royal contributor Victoria Murphy said. She has missed the event, which commemorates the contribution of British and Commonwealth military and civilian servicemen and women in the two World Wars for other reasons, in the past.
The queen's son, Charles, the prince of Wales, attended the event in her place Sunday, and placed a wreath at the memorial on her behalf. Charles' wife, Camilla, the duchess of Cornwall, and Prince William and Kate Middleton, the duke and duchess of Cambridge, also attended.
Others who attended included the earl and countess of Wessex, the princess royal and vice Admiral Sir Tim Laurence, the duke and duchess of Gloucester, the duke of Kent and Princess Alexandra.
Last month, the queen spent one night in the hospital for "preliminary investigations." She was released on Oct. 21 and was back at her desk at Windsor Castle that afternoon, according to a palace spokesperson.
The queen had also been scheduled to attend an evening reception on Nov. 1 at the 2021 United Nations Climate Change Conference, or COP26, in Glasgow, but had been advised by doctors to rest. Murphy said the queen's sprained back is unrelated to that advice.
Since doctors have advised Queen Elizabeth to rest, the royal household has scaled back her diary, keeping engagements light.