The Queen has sprained her back and is not able to attend the Remembrance Sunday service at the Cenotaph in London.
Buckingham Palace said the 95-year-old monarch made the decision on Sunday morning "with great regret" and is "disappointed" to miss the event.
It is understood the Queen's back sprain is unrelated to her doctor's recent advice to rest.
Buckingham Palace said: "The Queen, having sprained her back, has decided this morning with great regret that she will not be able to attend today's Remembrance Sunday Service at the Cenotaph.
"Her Majesty is disappointed that she will miss the service.
"As in previous years, a wreath will be laid on Her Majesty's behalf by the Prince of Wales.
"His Royal Highness, along with the Duchess of Cornwall, the Duke and Duchess of Cambridge, 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 will be present at the Cenotaph today as planned."