Genealogy
The dukes of Schleswig-Holstein-Sonderburg form a line of the House of Oldenburg; it consists of the male-line descendants of Duke John the Younger. The current royal houses of Denmark and Norway, as well as the future royal house of the United Kingdom (assuming Charles, Prince of Wales, will ascend to the crown) belong to the Schleswig-Holstein-Sonderburg line.
Read more about this topic: Schleswig-Holstein-Sonderburg