His Royal Highness Prince Philip, Duke of Edinburgh, has undergone a "successful procedure for a pre-existing heart condition" at St Bartholomew's Hospital, Buckingham Palace confirmed on Thursday.
"His Royal Highness will remain in hospital for treatment, rest and recuperation for a number of days," the royal family's representatives added.
Queen Elizabeth II's husband was admitted to King Edward VII's Hospital as a "precautionary measure" in February and then transferred to St Bartholomew's Hospital earlier this week.