Ernest Günther had a castle built in the years after 1651, which received the name of Augustenburg in honor of his wife, Auguste.

In 1764, Sønderborg castle, the seat of that elder Schleswig-Holstein branch, passed upon its owners' extinction into the hands of the Duke of Augustenburg, but against expectations it did not become a residence (they remained at Augustenborg).

The penultimate Duke of Augustenburg, also named Ernst Günther, allowed Sønderborg County Museum to move into a part of the castle in 1920.

An Augustenburg dynasty on a royal throne was however not to be, as Prince Christian August died a couple of months after his arrival in Sweden.

The Duke of Augustenburg was the next male-line heir to the royal house, though not descended in male line from Frederick III of Denmark and Norway.

Frederik August of Augustenburg attempted to proclaim himself reigning Duke Frederick VIII of Schleswig-Holstein in 1864, upon the final extinction of the senior branch of the Danish kings.