He became King in 1943 upon the sudden death of his father, King Boris III. Since he was still a minor, his uncle, Prince Kyril of Bulgaria was appointed regent. In 1944, Kyril and most of the senior members of his government were killed in a Soviet-backed coup, but Simeon was allowed to stay on the throne. A 1946 referendum voted to abolish the monarchy, but the royal family chose to flee the country rather than have Simeon abdicate.
In 2001 Simeon returned to Bulgaria, and was elected leader of the newly-formed National Movement for Simeon II. In elections held later that year the NMS won 119 out of 240 seats in Parliment, and Simeon became Prime Minister. He is the only monarch in history to regain political power through democratic election to a different office.
See also: List of Bulgarian monarchs