In 1893, King Alexander, aged seventeen, in a first coup d'état proclaimed himself of full age, dismissed the regents and their government, and took the royal authority into his own hands. His action was popular, and was rendered still more so by his appointment of a radical ministry.
In May 1894, King Alexander, by another coup, abolished the liberal constitution of 1889 and restored the conservative one of 1869. His attitude during the Greco-Turkish War (1897) was one of strict neutrality.
In the same year, the young King brought his father, Milan, back to Serbia and, in 1898, appointed him commander-in-chief of the Serbian army. During that time, Milan was regarded as the de facto ruler of the country.
In the summer of 1900, King Alexander suddenly announced his engagement to the widowed Madame Draga Mašin, formerly a lady-in-waiting to his mother. The projected union initially aroused great opposition: he did not consult with his father, who had been on vacation in Carlsbad and making arrangements to secure the hand of a German princess for his son, or his prime minister Dr. Vladan Đorđević, who was visiting the Paris Universal Exhibition at the time of the announcement. Both immediately resigned from their respective offices and Alexander had difficulty in forming a new cabinet. Alexander's mother also opposed the marriage and was subsequently banished from the kingdom.
Opposition to the union seemed to subside somewhat for a time upon the publication of Tsar Nicholas II's congratulations to the king on his engagement and of his acceptance to act as the principal witness at the wedding. The marriage was duly celebrated in August 1900. Even so, the unpopularity of the union weakened the King's position in the eyes of the army and the country at large.
King Alexander tried to reconcile political parties by unveiling a liberal constitution of his own initiative, introducing for the first time in the constitutional history of Serbia the system of two chambers (skupshtina and senate). This reconciled the political parties but did not reconcile the army which, already dissatisfied with the king's marriage, became still more so at the rumors that one of the two unpopular brothers of Queen Draga, Lieutenant Nikodije, was to be proclaimed heir-presumptive to the throne.
Meanwhile, the independence of the senate and of the council of state caused increasing irritation to King Alexander. In yet another coup d'état, he suspended (March 1903) the constitution for half an hour, time enough to publish the decrees by which the old senators and councillors of state were dismissed and replaced by new ones. This arbitrary act naturally increased the dissatisfaction in the country.
The conspirators searched the palace and eventually discovered the royal couple and murdered them in the early morning of June 11, 1903. King Alexander and Queen Draga were shot and their bodies mutilated and disemboweled and, according to eyewitnes accounts, thrown from a second floor window of the palace. The King was only 26 years old at the time of his death. King Alexander and Queen Draga were buried in the crypt of St. Mark's Church, Belgrade.