Peter I (; – 16 August 1921) was the last king of Serbia, reigning from 15 June 1903 to 1 December 1918. On 1 December 1918, he became the first king of the Serbs, Croats and Slovenes, and he held that title until his death three years later. Since he was the king of Serbia during a period of great Serbian military success, he was remembered by the Serbian people as King Peter the Liberator and also as the Old King. Peter was Karađorđe's grandson and third son of Persida Nenadović and Prince Alexander Karađorđević, who was forced to abdicate. Peter lived with his family in exile. He fought with the French Foreign Legion in the Franco-Prussian War. He joined as a volunteer under the alias Peter Mrkonjić in the Herzegovina uprising (1875–1877) against the Ottoman Empire. He married Princess Zorka of Montenegro, daughter of King Nicholas, in 1883. She gave birth to his five children, including Prince Alexander. After the death of his father in 1885, Peter became head of the Karađorđević dynasty. After a military coup d'état and the murder of King Alexander I Obrenović in 1903, Peter became King of Serbia. As king, he advocated a constitutional setup for the country and was famous for his liberal politics. The rule of King Peter was marked with the great exercise of political liberties, freedom of the press, national, economical and cultural rise, and it is sometimes dubbed a "golden" or "Periclean age". King Peter was the supreme commander of the Royal Serbian Army in the Balkan Wars. Because of his age, on 24 June 1914, he proclaimed his son, Prince Alexander, heir-apparent to the throne, as regent. In World War I he and his army retreated across the Principality of Albania. Early life Peter was born in Belgrade on , the fifth of Prince Alexander Karađorđević and his consort Persida Nenadović's ten children. He was the grandson of Karađorđe, the leader of the First Serbian Uprising (1804–1813) and the founder of the Karađorđević dynasty. Peter was not born in the Royal Court, which was undergoing renovations at the time, but at the home of merchant Miša Anastasijević. His birth was not met with much celebration because he was his parents' third son and his older brother Svetozar was the heir to the throne. His parents' oldest son, Aleksa, had died three years prior to Peter's birth, aged five,