Charles, the heir to the throne, was seen entering the rear entrance of the King Edward VII hospital in central London, wearing a face mask. He left after about 30 minutes.
Britain’s Prince Charles visited his father Philip in hospital on Saturday as the 99-year-old husband of Queen Elizabeth II receives precautionary treatment after falling ill this week.
Prince Philip, who turns 100 on June 10, was admitted on Tuesday. Sources say his admission was not coronavirus-related, and that he remains in good spirits.
The duke of Edinburgh, as he is formally known, is expected to remain in hospital into next week for observation and rest.
He was able to walk into the hospital unaided after arriving by private transport rather than ambulance, a source said at the time.