Prince Philip, the 90-year-old husband of Queen Elizabeth, was taken to a specialist heart hospital on Friday for tests after suffering chest pains, Buckingham Palace said.
Britain's longest-serving royal consort, known for his outspoken and sometimes brusque manner, was admitted to the Papworth Hospital, one of Britain's main heart and chest centres, in Cambridge, eastern England, a palace spokeswoman said.
He had been preparing to celebrate Christmas with other members of the royal family, reportedly including Prince William and his wife Catherine, at the Sandringham royal estate in eastern England.
He was taken to Papworth for precautionary tests after experiencing chest pains, the spokeswoman said. We don't have anything further to add at the moment. No more details of the condition of the Greek-born prince were immediately available. No one at the hospital was available for comment.
Philip had attended a lunch for staff a week ago and had been on very good form, the BBC reported.
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, former royal press spokesman Dickie Arbiter told the BBC.
Despite his age, Philip has generally been in good health and has continued a busy round of charity work and social engagements, recently visiting Australia and Ireland.
Philip, a pivotal figure in the House of Windsor, has a reputation as a fiercely loyal consort who prefers outdoor pursuits to introspection.
The Queen is monarch, but within the family setting, the Duke of Edinburgh is hugely important, royal commentator and author Penny Junor told Sky News.
He has always been the one who has called the shots in family matters. He has really made the major decisions.
Britain's tabloid newspapers have delighted over the years in recounting his many public gaffes.
He once told British students in China: If you stay here much longer, you'll be slitty-eyed.
Philip was accused by critics of being cruel to Princess Diana before her death in a car crash in Paris in 1997. However, the prince's aides rejected those claims at an inquest in 2007 and released letters purporting to show a close relationship between them.
Born on the Greek island of Corfu in 1921, Philip served in Britain's Royal Navy before marrying Elizabeth in 1947. They have four children, including the heir to the throne, Charles.
The prince has no clear-cut constitutional role. In private he is regarded as the unquestioned head of his family, but protocol obliges the man dubbed the second handshake to spend his public life one step behind his wife.
In a rare public tribute to her husband, the queen said in a speech in 1997: He is someone who doesn't take easily to compliments but he has, quite simply, been my strength and stay all these years, and I...owe him a debt greater than he would ever claim, or we shall ever know.
(Reporting by Peter Griffiths; editing by Andrew Roche)