Tsar Boris III of Bulgaria dies and is interred at Rila Monastery

Tsar Boris III of Bulgaria died unexpectedly on August 28, 1943, at his palace in Sofia following a brief illness. Official reports from the time, including statements by Prime Minister Bogdan Filov, attributed his death to a blocked left coronary artery, double pneumonia, and edema of the lungs and brain. Following his death, a 40-day national period of mourning was declared, and his son, Prince Simeon, ascended to the throne as Tsar Simeon II.

While official causes were medical, various historical theories regarding his death have persisted. Some accounts suggest potential poisoning, with theories involving Nazi Germany, the Soviet Union, or Italy. These speculations arose following his meetings with Adolf Hitler and his refusal to send Bulgarian troops against the USSR or deport Bulgarian Jews. Boris III was eventually buried at the Rila Monastery, where his heart is interred.