"Johann Wilhelm, Duke of Saxe-Jena (Jena, 28 March 1675 – Jena, 4 November 1690), was a duke of Saxe-Jena.
He was the youngest but sole surviving son ...
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of Bernhard II, Duke of Saxe-Jena by his wife Marie Charlotte, daughter of Henry de La Trémoille, 3rd Duke of Thouars, 2nd Duke of La Tremoille, and Prince of Talmond and Taranto." - (en.wikipedia.org 31.01.2020)