The Palace confirmed Prince Philip, 98, had been residing at the Royal Family's Sandringham estate, and left on Friday morning without Her Majesty.
The Duke of Edinburgh has spent his second night in hospital after being admitted to the King Edward VII Hospital in London.
"Britain's Prince Philip Has Been admitted to a London hospital Friday for" Monitoring and Therapy", Buckingham Palace has said in a statement.
Buckingham Palace said it was "a precautionary measure" on the advice of his doctor and that he was expected to remain in hospital for "a few days".
The source added the Duke entered the hospital walking.
The duke retired from official public duties two years ago.
"I'm told that Philip walked into hospital - there was no emergency admittance - and will probably stay in for a couple of days", the Daily Mail's royal correspondent Rebecca English tweeted Friday.
Pictured: The Queen, Prince Philip during the wedding ceremony of Britain's Prince Harry, Duke of Sussex and U.S. actress Meghan Markle in St George's Chapel, Windsor Castle, in Windsor, on May 19, 2018.
Speaking about the Duke's health in recent months, one source said: "The Duke has had a bad turn recently and has been looking much frailer of late".
She is expected to attend the same church on Christmas Day. Prince Philip also skipped Easter Sunday services a year ago ahead of the announcement that he underwent hip replacement surgery.
Lately the Queen has been pushed by chauffeur to the church on December 25 whereas different relations stroll the quick distance from Sandringham Home to hitch her.
The Queen knows that if her husband stays near her and in the center of the royal life, he will be obliged to get involve and that will defeat the objective of his retirement.
If he's discharged from the hospital in time, Philip will be part of the queen, Prince Charles, Duchess Camilla, Prince William, Duchess Kate and their children - Prince Louis, 6, Princess Charlotte, 4, and Prince Louis, nearly 20 months - to have a good time Christmas Eve and Christmas in Sandringham. The charity supports Armed Forces personnel and veterans, and their families at annual festive get-togethers across the charity's network of outreach centres.