Peter I (Serbian Cyrillic: Петар I Карађорђевић, romanized: Petar I Кarađorđević; 11 July [O.S. 29 June] 1844 – 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.

Princess Helen of Serbia (4 November [O.S. 23 October] 1884 – 16 October 1962) was a Serbian princess, the daughter of King Peter I of Serbia and his wife Princess Zorka of Montenegro.She was the elder sister of George, Crown Prince of Serbia and King Alexander I of Yugoslavia.Helen was also a niece of Princess Anastasia of Montenegro (or "Stana"), wife of Grand Duke …