Boris III, 1894–1943, czar of Bulgaria (1918–43), son of Czar Ferdinand, on whose abdication he succeeded to the throne. He ruled constitutionally until 1934, then set up a military dictatorship under his premier, Kimon Georgiev, and in 1935 began his personal dictatorship. He turned toward the Axis Powers and in 1940 forced Romania to restore southern Dobruja to Bulgaria. While visiting Hitler in Berlin, he agreed to declare war on Great Britain and the United States, but not on Russia. His mysterious death, possibly by heart attack or by assassination, soon followed. His son, Simeon II, succeeded under a regency.
"Boris III." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (February 19, 2018). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/boris-iii
"Boris III." The Columbia Encyclopedia, 6th ed.. . Retrieved February 19, 2018 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/boris-iii