Original: Established in 1672 for Bernhard, fourth son of Wilhelm, Duke of Saxe-Weimar, Saxe-Jena was reincorporated into Saxe-Weimar on the extinction of Bernhard's line in 1690.
Simplified: Part of the Duchy of Saxe-Weimar was given to Bernhard, the fourth son of Wilhelm, Duke of Saxe-Weimar in 1672.