AUGUSTENBURG AUGUSTENBORG (Dan).
A castle on the Danish island of Als (Alsen), off the eastern coast of the Duchy of Slesvig, built by Ernst Gunther (d.1689) and named after his wife, Auguste.
Ernst Gunther’s grandfather, Hans, a younger son of Christian III of Denmark, had founded the line of Schleswig-Holstein-Sonderburg, and his sons and grandsons founded several branches. The one descending from Ernst Gunther took its name from his castle and became the Dukes of Schleswig-Holstein-Sonderburg-Augustenburg.
It frequently happened among the princely houses of Europe that the longer the name of the family the less important was the Prince. This ceased to be true of the Augustenburgs in the 19th century, because not only did the vicissitudes of births, marriages and deaths wipe out the male lines senior to them in the Sonderburg line, but it became clear that the Danish royal line was going to die out of males too, leaving the Augustenburgs the heirs male to the Duchies of Schleswig and Holstein.
Although the Duke would also be the heir male of the Danish royal family, he was descended from an earlier King than Frederick III, with whom the Danish monarchy had become hereditary in 1661. The Duke was not in fact chosen as the heir to Denmark, and after a crisis in 1848-52 he also renounced his claims to Schleswig-Holstein, though this did not prevent many German nationalists, who wished to see the Duchies separated from Denmark, from continuing to favour an Augustenburg succession to the Duchies. Nor did the Duke’s renunciation prevent his son from pressing his own claims as the demise of the Danish royal line approached in 1863.
In the event Denmark was obliged to give up the Duchies in 1864 after war with Austria and Prussia. Prussia defeated Austria in 1866 and in 1867 absorbed Schleswig-Holstein, ignoring the claims of the Augustenburg heir. The male line of the Augustenburgs died out in 1931. The island of Als had returned to Denmark in 1920.