The position was first held by King Norodom Sihanouk in March 1945, during the French colonial administration. On 12 March 1945, Sihanouk collaborated with Imperial Japan and declared Cambodia's independence from France. On 18 March, he proclaimed himself prime minister and formed the first government which lasted until August 1945. He was succeeded by Son Ngoc Thanh until October 1945. Following the surrender of Japan, the French administration returned, ending the Japanese occupation.