He succeeded his father in 1917, during World War I, after the Entente Powers and the followers of Eleftherios Venizelos pushed King Constantine and his eldest son, Crown Prince George, into exile.

Alexander controversially married the commoner Aspasia Manos in 1919, provoking a major scandal that forced the couple to leave Greece for several months.

Alexander was born at Tatoi Palace on 1 August 1893 (20 July in the Julian calendar), the second son of Crown Prince Constantine of Greece and Princess Sophia of Prussia.

His father was the eldest son of King George I of Greece by his wife, Olga Constantinovna of Russia; his mother was the daughter of Frederick III, German Emperor, and Victoria, Princess Royal of the United Kingdom.

With his parents he undertook several trips abroad and regularly visited Schloss Friedrichshof, the home of his maternal grandmother, who had a particular affection for her Greek grandson.

[4] As a young officer, he was stationed, along with his elder brother, in the field staff of his father; and he accompanied the latter at the head of the Army of Thessaly during the capture of Thessaloniki in 1912.

[8] In 1915, at a party held in Athens by court marshal Theodore Ypsilantis, Alexander became re-acquainted with one of his childhood friends, Aspasia Manos.

Initially, Aspasia was resistant to his charm; although considered very handsome by his contemporaries, Alexander had a reputation as a ladies' man from numerous past liaisons.

[11] During World War I, Constantine I followed a formal policy of neutrality, yet he was openly benevolent towards Germany, which was fighting alongside Austria-Hungary, Bulgaria and the Ottoman Empire against the Triple Entente of Russia, France and Britain.

In July 1916, an arson attack ravaged Tatoi Palace and the royal family barely escaped the flames; Alexander was not injured but his mother narrowly saved Princess Katherine by carrying her through the woods for more than 2 km (1.2 mi).

The Allies, while determined to be rid of Constantine, did not wish to create a Greek republic, and sought to replace the king with another member of the royal family.

[15] The dismissal of Constantine was not unanimously supported by the Entente powers; while France and Britain did nothing to stop Jonnart's actions, the Russian provisional government officially protested to Paris.

The royals remained unpopular with the Venizelists, and Entente representatives advised the king's aunts and uncles, particularly Prince Nicholas, to leave.

Despite promises given by the Entente on Constantine's departure, the previous prime minister, Zaimis, was effectively forced to resign as Venizelos returned to Athens.

The majority of Thrace (previously split between Bulgaria and Turkey) and several Aegean Islands (such as Imbros and Tenedos) became part of Greece, and the region of Smyrna, in Ionia, was placed under Greek mandate.

[30] Despite their territorial gains following the Paris Peace Conference, the Greeks still hoped to achieve the Megali Idea and annex Constantinople and larger areas of Ottoman Asia Minor; they invaded Anatolia beyond Smyrna and sought to take Ankara, with the aim of destroying the Turkish resistance led by Mustafa Kemal (later known as Atatürk).

The Venizelists feared it would give Alexander a means to communicate with his exiled family through Colonel Manos and both sides of the political divide were unhappy at the king marrying a commoner.

[34][c] When Prince Arthur, Duke of Connaught and Strathearn, visited Athens in March 1918, to confer the Order of the Bath upon the king, Alexander feared that a marriage between him and Princess Mary of the United Kingdom would be discussed as part of an attempt to consolidate the relationship between Greece and Britain.

[11] The British authorities feared that Alexander would abdicate in order to marry Aspasia if the wedding was blocked, and they wanted to avoid Greece becoming a republic in case it led to instability or an increase in French influence at their expense.

[10] With the help of Aspasia's brother-in-law, Christo Zalocostas, and after three unsuccessful attempts, the couple eventually married in secret before a royal chaplain, Archimandrite Zacharistas, on the evening of 17 November 1919.

[28] On their Parisian honeymoon, while motoring near Fontainebleau, the couple witnessed a serious car crash in which Count de Kergariou's chauffeur lost control of his master's vehicle.

[45] On 7 September, Venizelos, counting on a surge of support in the wake of the signing of the Treaty of Sèvres and the expansion of Greek territory, announced a general election for early November.

[49] On 19 October, he became delirious and called out for his mother, but the Greek government refused to allow her to re-enter the country from exile in Switzerland, despite her own protestations.

[h] The Hellenic Parliament demanded that Constantine I and Crown Prince George be excluded from the succession but sought to preserve the monarchy by selecting another member of the royal house as the new sovereign.

[56] Paul, however, refused to become king while his father and elder brother were alive, insisting that neither of them had renounced their rights to the throne and that he therefore could never legitimately wear the crown.

[57] The throne remained vacant and the legislative elections of 1920 turned into an open conflict between the Venizelists, who favored republicanism, and the supporters of the ex-King Constantine.

[58] On 14 November 1920, with the war with Turkey dragging on, the monarchists won, and Dimitrios Rallis became prime minister; Venizelos (who lost his own parliamentary seat) chose to leave Greece in self-exile.

[59] Under the restored King Constantine I, whose return was endorsed overwhelmingly in a referendum, Greece went on to lose the Greco–Turkish War with heavy military and civilian casualties.

Alexander's death in the midst of an election campaign helped destabilize the Venizelos regime, and the resultant loss of Allied support contributed to the failure of Greece's territorial ambitions.

Initially, the government took the line that since Alexander had married Aspasia without the permission of his father or the church, his marriage was illegal and his posthumous daughter was illegitimate.