Britain's 91-year-old Duke of Edinburgh, husband of Queen Elizabeth, was taken to hospital in Scotland on Wednesday as a "precautionary measure", Buckingham Palace said.
"He was taken to Aberdeen Royal Infirmary as a precautionary measure," a Palace spokeswoman said. "We don't have any further details and are waiting for the Duke to be medically assessed."
Two months ago, Prince Philip was taken to hospital with a bladder infection, overshadowing four days of celebrations for the Queen's 60th year on the British throne.
In December last year, Philip had an operation to clear a blocked heart artery and spent Christmas in hospital.