Duchy of Saxe-Altenburg
In 1640 the sons of the late Ernestine duke John II of Saxe-Weimar divided their paternal heritage ("Ernestinische Teilung") whereby Duke Ernest the Pious, a younger son, received the newly established Duchy of Saxe-Gotha. In 1636 Ernest had married Elisabeth Sophie, the only child of Duke John Philip of Saxe-Altenburg. Upon her father's death in 1639, the Duchy of Saxe-Altenburg passed to her uncle Duke Frederick William II and her cousin Frederick William III.