Prince Philip was admitted to hospital for an exploratory abdominal operation on Thursday evening.
The Duke of Edinburgh was taken to the Harley Street”s London Clinic shortly after making an appearance at the Queen”s garden party at Buckingham Palace.
The Duke, who turns 92 on 10 June, is expected to remain there for up to two weeks.
The Queen”s husband missed an engagement on Monday night because he was feeling “under the weather”.
“He is in very good health,” a Buckingham Palace spokesperson said. “He felt unwell on Monday and missed an engagement but that was down to the fact he had temporarily lost his voice.”
His admission to hospital was planned for after the garden party.
The Palace said in a statement that “further updates will be issued when appropriate”.
The Queen will still conduct her engagements as planned on Friday, which include a visit to the new BBC studios in London.