(CNN) -- Prince Philip, husband of Britain's Queen Elizabeth II, has been admitted to a London hospital "for an exploratory operation," Buckingham Palace said Thursday.
The Duke of Edinburgh is expected to stay in the hospital for up to two weeks, according to the palace statement. He is being treated at the London Clinic "following abdominal investigations."
The operation likely will take place Friday, a spokesman said.
The 91-year-old is set to celebrate his next birthday Monday.
The prince showed no signs of feeling ill Thursday at a presentation at Buckingham Palace, according to the Press Association. The news agency reported Philip was joking and laughing with guests at a ceremony where the queen made him a member of the Order of New Zealand.
Tuesday, he and other members of the royal family attended a service at Westminster Abbey to mark the 60th anniversary of Queen Elizabeth II's coronation.
Philip left Greece a year after he was born there, following the 1922 overthrow of his brother, King Constantine I. Despite his roots in that country, he has a mixed ancestry and, like his wife, is a great-great-grandchild of Britain's Queen Victoria.
A Royal Air Force veteran, he met Elizabeth in 1939 and married her in November 1947. They have four children.
In addition to his royal and military duties, Philip has served as president of the World Wildlife Fund and the International Equestrian Foundation.
Philip has had a number of documented health problems in recent years, including treatment for a blocked coronary artery in December 2011 and a hospitalization in June 2012 for a bladder infection. He was admitted again to a hospital -- this time in Scotland -- for treatment of the latter ailment two months later.
CNN's Max Foster contributed to this report.