He was often described as a champion of European unity.
Otto Habsburg-Lothringen, the eldest son of the last Austrian emperor, has died at the age of 98.
He lived in southern Germany during a life spent mostly in exile.
The Habsburgs were the ruling family of the Austro-Hungarian empire, which collapsed at the end of World War One.
Austria abolished the monarchy and the man also known as Otto von Habsburg gave up his claim to the throne in 1961.
He was a member of the European Parliament for the German state of Bavaria and gave speeches around the world on European and global politics.
In one tribute, the former Austrian chancellor Wolfgang Schuessel called him a “great patriot” who “incorporated pan-European thinking like no other”.