The former King of Greece, Constantine II died after treatment in an intensive care unit, staff at the Hygeia Hospital in Athens have confirmed to The Associated Press.
While there are no further details about an official announcement, his doctors announced the former King died on Tuesday.
Constantine II was known in Greece as a youthful prince having acceded to the throne at the age of 23 in 1964.
After the collapse of the monarchy, the former King of Greece lived in Hampstead Garden Suburb, London, and was said to be close to his second cousin Charles, who is now King Charles III of England.
In his final days of accepting Greece as a republic, Constantine continued to style himself King of Greece and his children as princes and princesses despite Greece no longer recognising titles of royal nobility.
He is survived by his wife, the former Princess Anne-Marie of Denmark, youngest sister of Queen Margrethe II; five children, Alexia, Pavlos, Nikolaos, Theodora and Philippos; and nine grandchildren.
Source: Ekathimerini