The Duke of Edinburgh will have hip surgery on Wednesday after he was admitted to hospital for the planned procedure, Buckingham Palace has said.
Philip is understood to have had trouble with the hip for about a month and will now be operated on to resolve the problem.
The Queen, who is at Windsor Castle for the traditional Easter Court, is being kept fully informed about the treatment of the duke who was admitted to the private King Edward VII hospital in Marylebone, central London on Tuesday.
Details of the duke's condition, or which joint is causing the issue, have not been released by Buckingham Palace but the late Queen Mother underwent two successful hip operations in the 1990s, first when aged 95 then later when she was 97.
But Philip does not walk with the aid of a stick as the Queen Mother did and was spotted last week driving himself around Windsor Great Park, leading to speculation he may have a problem with torn cartilage.
Buckingham Palace said in a short statement: "His Royal Highness the Duke of Edinburgh was admitted to King Edward VII Hospital in London this afternoon, for planned surgery on his hip which will take place tomorrow."
The duke's hip problem forced him to miss the annual Maundy Service with the Queen last week which this year was staged at Windsor Castle's St George's Chapel.
And earlier last month the duke did not attend an event with the Duke of York and Queen because he was reportedly "under the weather".
But the Duke has generally been of good health throughout his life and has kept active well into his later years and is thought to be keeping busy now he has effectively retired from royal duties.
There maybe be some concern for the duke given his age, but Scarlett McNally, an orthopaedic surgeon and council member of the Royal College of Surgeons, said: "Any operation and any anaesthetic carries some risk.
"What is most important is someone's fitness, as in their heart and lung fitness, how much exercise they do and how well nourished they are. That's more important than someone's chronological age."
The duke stepped down from his public duties last summer, but on occasion does attend events with the Queen.
When it was announced last year that he would be retiring from official engagements, Buckingham Palace stressed that the decision was not health-related and he had the full support of the Queen.
King Edward VII is the private hospital of choice for the royal family and has been treating members of the monarchy for decades.
It was founded in 1899 at the suggestion of the then-Prince of Wales, and has treated most senior members of the royal family, including the Queen, Prince of Wales and the Duke of Cambridge.