Augusta of Saxe-Weimar-Einsach was just another German princess who became Queen of Prussia. But after the unification of Germany, she became an Empress.
Augusta of Saxe-Weimar-Eisenach: The First German Empress

Augusta of Saxe-Weimar-Einsach was just another German princess who became Queen of Prussia. But after the unification of Germany, she became an Empress.