The Duke of Edinburgh Prince Philip is in hospital after having surgery for a blocked coronary artery, according to a spokesperson for Buckingham Palace.
The 90-year-old has a successful "invasive procedure of coronary stenting" at the UK's largest specialist cardiothoracic unit, Papworth Hospital in Cambridge. He is expected to stay in hospital for some time following the procedure.
Buckingham Palace said in a short statement: "Following tests at Papworth Cardiothoracic Hospital in Cambridge this evening the Duke of Edinburgh was found to have a blocked coronary artery which caused his chest pains.
"This was treated successfully by the minimally invasive procedure of coronary stenting. Prince Philip will remain in hospital under observation for a short period."
Prince Philip was rushed from from royal retreat Sandringham to the hospital on Friday evening, with a place spokesperson saying he was suffering from chest pains.
The Duke, who married the Queen in 1947, has four children with the monarch.
Dickie Arbiter, a former press secretary to the Queen, said that he was in "pretty good health" for his age.
"He has had these chest pains before and I don't think it's anything untoward, but given his age they are being safe rather than sorry.
"I am sure we are going to see him on Christmas Day and he can look forward to accompanying the Queen in the new year," Arbiter told Sky News.
Dr Simon Davies, consultant intervention cardiologist at the Royal Brompton Hospital in London, told the Press Association he may have a heart problem. The cardiologist said it was "impossible to say" how long Philip could be kept in hospital.
But he added: "The fact is he must have looked after himself to be looking so well."
"You just have to be suspicious that it's the heart just because he is a man and he is 90."
The UK's longest serving royal consort pulled out of a trip to Italy in October because he had a cold.
Prince Philip and his family had been planning to spend the weekend celebrating a traditional Christmas, before the Queen's Diamond Jubilee next year.
Members of the royal family will fly around the world to celebrate the monarch's 60 years on the throne in 2012.