Schleswig-Holstein-Sonderburg was the name of a branch line of the House of Oldenburg as well as the name of their land. It existed from 1564 until 1668 and was a titular duchy under the King of Denma
Coat of arms of the Dukes of Schleswig-Holstein-Sonderburg
The Duchy of Schleswig-Holstein-Sonderburg was founded by John III and fragmented after his death into numerous mini-states
Hans the Younger was the duke of Schleswig-Holstein-Sonderburg.
Schleswig-Holstein-Sonderburg
…and Holstein with his two brothers, each receiving a third of the royal estate in Schleswig and Holstein. Sonderburg was the portion received by Duke John III, called "the Younger". His domain included inter alia the territories of Sonderburg, Norburg, Ærø, Plön and Ahrensbök together with their assigned Ämter…
Escutcheon of Hans the Younger in the chapel of Sønderborg Castle.