Prince Philip is "progressing satisfactorily" after an exploratory abdominal operation on Friday, Buckingham Palace has said.
The statement said the results from the scheduled surgery will now be analysed.
The Queen's husband, who turns 92 on Monday, was admitted to the London Clinic on Thursday evening and is expected to stay in hospital for about two weeks.
Her Majesty, who is said to be concerned and being kept informed, will spend the weekend at Windsor Castle, according to the BBC.
She continued with her planned engagements on Friday and officially opened the BBC's rebuilt Broadcasting House in London on Friday afternoon.
Crowds had gathered to welcome the beloved royal, 87, who looked elegant in a powder blue coat and hat, and hundreds of BBC staff lined an open atrium for her arrival, with some cheering as she stepped from her chauffeur-driven limousine.
She began her tour by visiting BBC Radio 1 and meeting presenters including Nick Grimshaw, Trevor Nelson and Sara Cox. She then visited the station's famous Live Lounge to watch a performance by The Script, whose lead singer Danny O'Donoghue is a judge on The Voice.
The Duke of Edinburgh was taken to the Harley Street clinic shortly after making an appearance at the Queen's garden party at Buckingham Palace on Thursday afternoon. His admission to hospital comes after he 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."
Philip and the Queen appeared on the steps of the Palace at 4pm when the national anthem was played to mark the start of the third of the summer garden parties. Onlookers reported Philip being in good spirits as he mingled with invitees.
On Wednesday, he toured a Victorian steamship, the SS Robin, in London's East End. It was a very personal visit for the former sailor who led a campaign against the vessel being scrapped in the 1970s.
It's a little princess!