PHOTO: Britain's Prince Philip, in his role as Captain General, Royal Marines, attends a Parade to mark the finale of the 1664 Global Challenge, on the Buckingham Palace Forecourt, in central London, Britain, Aug. 2, 2017.
PHOTO: HRH Prince Philip, Duke of Edinburgh, wearing his military dress uniform, circa 1990.
Prince Philip, Duke of Edinburgh and the husband of Queen Elizabeth II, fought in World War II with the Royal Navy before his marriage, during which he has become known for consistently supporting his wife during her reign.
PHOTO: Prince Philip waves as he is driven away from King Edward VII's Hospital in central London, April 13, 2018.
PHOTO: Princess Anne leaves the King Edward VII's Hospital after visiting her father Prince Philip in London, April 12, 2018.
PHOTO: Britain's Prince Philip, Duke of Edinburgh leaves after attending Royal Family's traditional Christmas Day church service at St Mary Magdalene Church in Sandringham, England, Dec. 25, 2017.
Britain's Prince Philip waves as he leaves the King Edward VII Hospital, after recovering from a planned surgery last Wednesday, in London, Friday, April 13, 2018. (Victoria Jones/PA via AP)
Britain's Princess Anne leaves the King Edward VII Hospital in London, Thursday, April 12, 2018. Princess Anne has visited her father Prince Philip in the hospital where he is recovering from hip replacement surgery. She visited 96-year-old Philip at
A police officer stands guard as a man approaches the entrance of King Edward VII Hospital in London, Wednesday, April 4, 2018. The elderly husband of Queen Elizabeth II is set to undergo hip surgery in a London hospital. Prince Philip, 96, has been