The Dukes of Schleswig - Holstein - Sonderburg - Glücksburg constitute the senior male line of the family , hold headship by primogeniture of both the House of Glücksburg and the entire House of Oldenburg .
The Dukes of Schleswig - Holstein - Sonderburg - Glücksburg constitute the senior male line of the family . 
 They hold the headship by primogeniture of both the House of Glücksburg and the entire House of Oldenburg .