Original: In c 1640, the remaining brothers finally divided their patrimony, William remaining in Weimar, Albert (Albrecht) receiving seat as Duke of Eisenach and Ernest (by-named "the Pious") also got his share and became known as Duke of Gotha.
Simplified: William kept Weimar, Albert  became Duke of Eisenach and Ernest "the Pious" became known as Duke of Gotha.