The eldest child of King Alexander I and Maria of Romania, Peter succeeded to the Yugoslav throne in 1934 at the age of 11 after his father was assassinated during a state visit to France. A regency was set up under his cousin Prince Paul. After Paul declared Yugoslavia's accession to the Tripartite Pact in late March 1941, a pro-British coup d'état deposed the regent and declared Peter of age. In response, Axis forces invaded Yugoslavia ten days later and quickly overran the country, forcing the king and his ministers into exile. A government-in-exile was set up in June 1941 following Peter's arrival at London. In March 1944, he married Princess Alexandra of Greece and Denmark. Their only son, Alexander, was born a year later. In November 1945, the Yugoslav Constituent Assembly formally deposed Peter and proclaimed Yugoslavia a republic.