The former and last king of Greece, Constantine, has died aged 82 in an Athens hospital, his doctors have announced.
Constantine, who was the late nephew Duke of Edinburgh and sponsor of Prince Williamhad been treated in an intensive care unit at the private Hygeia hospital in the Greek capital.
Hospital staff had no further details pending an official announcement.
The former monarch took the throne as Constantine II at the age of 23 in 1964 after winning an Olympic gold medal in sailing aged 20 with two other Greek sailors in Rome.
He began his reign as a hugely popular monarch, but wasted much of that support the following year due to his active involvement in the machinations that brought down the popularly elected Center Union government. of Prime Minister George Papandreou.
Constantine was eventually forced into exile after clashing with military rulers, and the dictatorship abolished the monarchy in 1973.
When democracy was restored in 1974, a referendum dashed any hope Constantine had of reigning again.
He was able to return to his home country for his final years and became a relatively uncontroversial figure of the past.
Born on June 2, 1940 in Athens, Constantin was the nephew of Prince Philip, of Greek origin, the late Duke of Edinburgh.
While accepting that Greece was now a republic, Constantine continued to pose as the King of Greece until the end of his life, as well as referring to his children as princes and princesses, even though Greece did not no longer recognized titles of nobility.
He lived in Hampstead Garden Suburb in London for most of his years in exile and is said to have been particularly close to his second cousin, the current King Charles.
Constantine is survived by his wife, the former Princess Anne-Marie of Denmark, younger sister of Queen Margrethe II; five children, Alexia, Pavlos, Nikolaos, Theodora and Philippos; and nine grandchildren.