Who was the last Emperor of Austria-Hungary?

Charles I, the great-nephew of Franz Joseph I, became Emperor in 1916 when Franz Joseph I died at the age of 86. His reign ended with the collapse of the empire at the end of the First World War in late 1918. He did not abdicate, but "renounced participation" in state affairs and went into exile. He was involved in attempts to regain the Hungarian throne in 1921, but failed. He died in 1922 at the age of 34 from respiratory failure while in Madeira, Portugal.

He became the heir apparent of Franz Joseph in 1914 when his uncle, Archduke Franz Ferdinand was assassinated in Sarajevo, the starting point of the First World War. He participated in the early part of the war, eventually promoted to Field Marshal in command of troops first on the Italian front, then on the eastern front.

After he became Emperor, he entered secret negotiations with France, using his brother-in-law, Prince Sixtus of Bourbon-Parma, as an intermediary. But no results came of the effort. Civil unrest and tension between ethnic groups sealed the fate of Austria-Hungary as different nationalities broke away from the empire.

Charles was beatified by Pope John Paul II in 2004, in part for his role in trying to negotiate peace with France. He is known to the Catholic Church as Blessed Karl of Austria.