The Principality of Bulgaria was established in 1878 as a result of the Treaty of Berlin, as a vassal state of the Ottoman Empire.  Prince Alexander of Battenberg was elected as the first Prince.  He would resign several years later, and be replaced by Prince Ferdinand of Saxe-Coburg and Gotha.

In 1908, Ferdinand declared Bulgaria a fully-independent Kingdom, naming himself as Tsar.  His heirs would remain on the Bulgarian throne until the abolition of the monarchy in 1946.

Principality of Bulgaria
1879-1886     Prince Alexander I
1887-1908     Prince Ferdinand I

 Kingdom of Bulgaria
1908-1918     Tsar Ferdinand I
1918-1943     Tsar Boris III
1943-1946     Tsar Simeon II (monarchy abolished)