Carol I of Romania , original name Prince Karl Eitel Friedrich Zephyrinus Ludwig of Hohenzollern-Sigmaringen , later simply of Hohenzollern ( April 20th , 1839 - ) , German prince , was elected Domnitor ( Prince ) of Romania on April 20th , 1866 , following the overthrow of Alexandru Ioan Cuza . He was elected prince of Romania on 20 April 1866 following the overthrow of Alexandru Ioan Cuza by a palace coup .