Constantine II (born June 2, 1940) reigns as the King of Greece from 1964 until the abolition of the monarchy in 1973.

He accedes as king following the death of his father King Paul in March 1964.

Later this year he marries Princess Anne-Marie of Denmark with whom he eventually has five children.

Although the accession of the young monarch is initially regarded auspiciously, his reign soon becomes controversial: ongoing political instability culminates in the Colonels' Coup of 21 April 1967.

The coup is successful, leaving Constantine, as the head of state, little room to maneuver since he has no loyal military forces on which to rely.

As a result, he reluctantly agrees to inaugurate the Greek military junta of 1967–1974 on the condition that it be made up largely of civilian ministers.

On December 13, 1967, Constantine is forced to flee the country, following an unsuccessful countercoup against the junta.

He remains (formally) the head of state in exile until the junta conducts the July 29, 1973, Greek republic referendum, which abolishes the monarchy.

There are questions concerning the validity of this referendum and whether people are pressured to vote for a republic.

Therefore a fresh referendum is held after the restoration of democracy in 1974.

This second referendum is held after the fall of the junta as the 1974 Greek republic referendum on December 8, 1974, and confirms the abolition of the monarchy and the establishment of the Third Hellenic Republic.

Constantine, who is not allowed to return to Greece to campaign, accepts the results of the plebiscite.

Constantine is also a former competitive sailor and Olympian, winning a gold medal in the 1960 Rome Olympics in the Dragon class, and later serving on the International Olympic Committee.