Duchy of Prussia
The Electors of Brandenburg inherited the Duchy of Prussia upon Albert Frederick's death in 1618, but the duchy continued to be held as a fief under the Polish Crown until 1656/7. Since John Sigismund had suffered a stroke in 1616 and as a consequence was severely handicapped physically as well as mentally, his wife Anna ruled the Duchy of Prussia in his name until John Sigismund died of a second stroke in 1619, aged 47.