Friedrich Ferdinand, Duke of Schleswig-Holstein-Sonderburg-Glücksburg, then Friedrich Ferdinand, Duke of Schleswig-Holstein (12 October 1855 – 21 January 1934), was the fourth
^H. Sandner, in his biography of his son-in-law, Carl Eduard of Saxe-Coburg and Gotha, Hitlers Herzog (2010), states on p. 257 that Friedrich Ferdinand dies at Primkenau, Silesia (now Przemków, Poland).
^Hof- und Staats-Handbuch des Herzogtum Anhalt (1894) "Herzoglicher Haus-orden Albrecht des Bären" p. 17
^Bille-Hansen, A. C.; Holck, Harald, eds. (1900) [1st pub.:1801]. Statshaandbog for Kongeriget Danmark for Aaret 1900 [State Manual of the Kingdom of Denmark for the Year 1900] (PDF). Kongelig Dansk Hof- og Statskalender (in Danish). Copenhagen: J.H. Schultz A.-S. Universitetsbogtrykkeri. pp. 3–4. Retrieved 30 April 2020 – via da:DIS Danmark.