The former king was deposed by a military junta in 1973, with his nine-year reign coinciding with one of the most turbulent periods in Greece's political history.
Greece's last and former king, Constantine II, died on Tuesday aged 82, state website ERT news reported.
The late king, the only son of King Paul and Queen Frederica of Greece, ascended to the throne in 1964. His nine-year reign coincided with one of the most turbulent periods in the country's political history, with a military coup on 21 April 1967 resulting in the installation of a right-wing military dictatorship, commonly known as the 'Regime of the Colonels'.
A few months later, Constantine was forced to flee Greece after leading an unsuccessful countercoup against the then military junta.
The late king remained in Rome until the regime abolished the monarchy in 1973.
But upon the junta's fall in 1974, things would not revert to how they were before. In a referendum called by a national unity government led by Konstantinos Karamanlis, Greeks rejected the monarchy for a second time, making Constantine the country's last king. Athens later stripped him of his citizenship.
In 2002, Constantine and other members of his family were compensated with €13.7 million for their former property in Greece, which includes the Tatoi palace estate north of Athens -- that is currently being restored -- and a villa in Corfu, the birthplace of the late Prince Philip, Duke of Edinburgh and now a museum.
The former king was married to Queen Anne-Marie of Greece and leaves behind five children. He is also Prince William's godfather, having lived in London for years before returning to Greece.
An accomplished athlete and competitive sailor, Constantine's team won a gold medal at the 1960 Olympics.
In his last public appearance in the centre of Athens last year, the former king was seen in a wheelchair and with nasal catheters, accompanied by his sister, the former Queen of Spain Sofia, and other relatives.
Suffering from chronic heart and mobility problems, the Constantine's health condition had worsened and he had been hospitalised various times in recent months.