Who married Peter I of Serbia?

Peter I (Serbo-Croatian: Петар I Карађорђевић, romanized: Petar I Karađorđević; 11 July [O.S. 29 June] 1844 – 16 August 1921) was King of Serbia from 15 June 1903 to 1 December 1918. On 1 December 1918, he became 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 Serbians as King Peter the Liberator and also as the Old King.

Peter was the fifth child and third son of Alexander Karađorđević, Prince of Serbia, and his wife, Persida Nenadović. Prince Alexander was forced to abdicate in 1858, and 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 (Serbian Cyrillic: Петар Мркоњић, romanized: Petar Mrkonjić) in the Herzegovina uprising (1875–1877) against the Ottoman Empire. In 1883, Prince Peter married Princess Ljubica, daughter of King Nicholas I of Montenegro. Ljubica became known as Princess Zorka upon her marriage. Peter and Zorka had five children: Helen, Milena, George, Alexander, and Andrew. After his father died in 1885, Peter became head of the Karađorđević dynasty.

After King Alexander I Obrenović was murdered during the May Coup of 1903, Peter Karađorđević became the new king of Serbia. As king, he advocated a constitutional setup for the country and was famous for his liberal politics. Peter's rule 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". Peter was the supreme commander of the Royal Serbian Army in the Balkan Wars. On 24 June 1914, the aging king proclaimed his son and heir Alexander as regent. In World War I, the King and his army retreated across the Principality of Albania. Peter died in 1921 aged 77.

Princess Zorka Karađorđević (Serbian Cyrillic: Кнегиња црногорска Зорка; 23 December [O.S. 11 December] 1864 – 16 March [O.S. 4 March] 1890), born Princess Ljubica of Montenegro, was the eldest child of Prince Nicholas I and Princess Milena of Montenegro, who later became the country's king and queen consort. In 1883, Ljubica married Prince Peter Karađorđević and she changed her name to Zorka (and her surname to Karađorđević). She died in childbirth while giving birth to Prince Andrija on 16 March 1890. Prince Andrija died shortly thereafter. Zorka's husband later became king of Serbia as Peter I.