Buckingham Palace says Prince Philip, 90-year-old husband of Queen Elizabeth II, has been hospitalized with a bladder infection.
Monday's announcement comes as the U.K. is celebrating the queen's Diamond Jubilee.
The palace said he had been taken to hospital as "a precautionary measure" and would remain under observation for a few days, meaning that he will miss the latter part of the queen's Diamond Jubilee celebrations.
The palace said the prince, who will turn 91 on Saturday, was taken to the King Edward VII Hospital in London from Windsor Castle. It said he would remain in hospital under observation for a few days.
British music royalty was set to celebrate Queen Elizabeth II on Monday with a Buckingham Palace concert featuring acts from throughout her 60-year-reign. Philip will miss the concert.
On Sunday, Prince Philip joined the queen and senior royals on the River Thames in cold and blustery weather for a pageant in honor of Elizabeth's 60 years on the throne.
The prince, who married then then-Princess Elizabeth in 1947, has cut back on official engagements in recent years, but still maintains a busy schedule. He spent four nights in the hospital at Christmas after suffering chest pains, and underwent a successful coronary stent procedure to clear a blocked artery.
He has been at the queen's side during engagements across Britain to mark the jubilee, and appeared in good spirits as he traveled down the river on a barge Sunday, despite the harsh weather.
The palace said Philip was "understandably, disappointed about missing this evening's Diamond Jubilee Concert," as well as a St. Paul's Cathedral service and other jubilee events planned for Tuesday.
The Associated Press contributed reporting to this story.