Prince Michael of Greece and Denmark, who was Prince Philip’s first cousin, died at the age of 85, his family confirmed on Sunday.
The final living grandson of George I of Greece died in an Athens hospital and is set to be buried in the capital on Thursday.
As well as his royal status, Michael was also a respected historian, publishing under the name Michel De Gres.
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Notably, Michael renounced his right to the Greek throne in 1965 to wed his wife Marina Karella, who was not royalty.
He recalled his love for Marina in his memoir Prince Michael of Greece: Crown, Art, and Fantasy.
“She was just so lovely and gracious with me. It didn’t take long to decide that I wanted to marry her,” he wrote.
It took Michael two years to negotiate the marriage.
“I remember I was dancing with her at a party, and I just looked at her. It was like a revelation — it was her and no one else,” he said last year.
The Greek prince was the only child of Prince Christopher, the younger brother of Prince Philip’s father, Prince Andrew.
After finishing school, Michael studied political science in Paris before serving a term in the Hellenic Coast Guard, the national coast guard of Greece.
Michael started his career as a historian in 1970, writing about historical subjects including Ancient Greece, the Ottoman Empire and European royal families.
He published fictional biographies and French novels throughout his career.
He is survived by his wife and their two daughters, Princess Olga of Savoy-Aosta and Princess Alexandra of Greece.