An Olympic gold medallist in sailing at the 1960 Rome Olympics, he reigned from 1964 until the proclamation of the Republic in 1974, which coincided with the end of the regime of the Colonels (1967-1974).
In 1968, eight months after the military coup, he attempted a counter-coup which failed. Constantine then fled with the royal family to Rome and subsequently moved to England in 1974. In a referendum after the return of democracy, nearly 70% of Greeks voted to abolish the monarchy. Connected to the British and Danish monarchies, the dynasty Schleswig-Holstein-Sonderburg-Glücksburg, started by Constantine's Danish grandfather George I, in 1863, ends with him. (ANSAmed).