Hermann's younger brother subsequently served as heir presumptive to the Grand Duchy of Saxe-Weimar-Eisenach until the birth of William Ernest's eldest son.

Wilhelm Ernst created the new Weimar town centre under the direction of Hans Olde, Henry van de Velde, and Adolf Brütt.

The birth of Wilhelmina's daughter Juliana in 1909 lessened the chance for any member of the House of Wettin (Saxe-Weimar-Eisenach branch) to inherit the Dutch throne.

On 9 November 1918, Grand Duke Wilhelm Ernst - along with the rest of the German monarchs following the defeat of Germany in World War I - was forced to abdicate.

In Meiningen on 21 January 1910, Wilhelm Ernst married second to Princess Feodora of Saxe-Meiningen, daughter of Prince Friedrich Johann of Saxe-Meinigen.