Ernest Günther had a castle built in the years after 1651, which received the name of Augustenborg in honor of his wife, Auguste. She was also from a branch of the Dukes of Schleswig-Holstein as a daughter of Philip (1584–1663), Duke of Glücksburg. As that castle became the chief seat of their line, the family eventually used the name of Augustenborg as its branch name. As they were agnates of the ducal house, the title of duke belonged to every one of them (as is the Germanic custom).