Boris III (1894 - 28 August 1943), Tsar of the Kingdom of Bulgaria from 1918 until his death in 1943. The eldest son of Ferdinand I, Boris assumed the throne upon the abdication of his father in the wake of Bulgaria's defeat in World War I. Following the outbreak of World War II, Bulgaria initially remained neutral. In 1940, Bogdan Filov replaced Kyoseivanov as prime minister, becoming the last prime minister to serve under Boris. In January 1941, Boris approved the anti-Semitic Law for Protection of the Nation, which denied citizenship to Bulgarian Jews and placed numerous restrictions upon them. In March 1941, Bulgaria joined the Axis. Boris refused to participate in the German invasion of the Soviet Union and largely resisted German attempts to deport Bulgarian Jews as part of the Holocaust. In August 1943, shortly after returning from a visit to Germany, Boris died at the age of 49. His six-year-old son, Simeon II, succeeded him as tsar.