Question: Who is the maternal grandfather of Princess Helena Adelaide Of Schleswig-Holstein-Sonderburg-Glücksburg?

Knowledge 1: Princess Helena Adelaide of Schleswig-Holstein-Sonderburg-Glücksburg
Princess Helena Adelaide of Schleswig-Holstein-Sonderburg-Glücksburg (1 June 1888 - 30 June 1962) was the third eldest daughter of Friedrich Ferdinand, Duke of Schleswig-Holstein and his wife Princess Karoline Mathilde of Schleswig-Holstein-Sonderburg-Augustenburg.She was a princess of Denmark through her marriage within the House of Schleswig-Holstein-Sonderburg-Glücksburg to Prince Harald of Denmark.Princess Helena was a Nazi sympathiser during World War II and was after the war exiled from Denmark, but eventually allowed to return, where she died. [SEP] Knowledge 2: Princess Karoline Mathilde of Schleswig-Holstein-Sonderburg-Augustenburg
Princess Karoline Mathilde of Schleswig-Holstein-Sonderburg-Augustenburg (25 January 1860, in Augustenborg, Jutland, Denmark – 20 February 1932, in Grünholz, Province of Schleswig-Holstein, Free State of Prussia, Weimar Republic) was the second-eldest daughter of Frederick VIII, Duke of Schleswig-Holstein and his wife Princess Adelheid of Hohenlohe-Langenburg.
Knowledge 1: Princess Helena Adelaide of Schleswig-Holstein-Sonderburg-Glücksburg
Princess Helena Adelaide of Schleswig-Holstein-Sonderburg-Glücksburg (1 June 1888 - 30 June 1962) was the third eldest daughter of Friedrich Ferdinand, Duke of Schleswig-Holstein and his wife Princess Karoline Mathilde of Schleswig-Holstein-Sonderburg-Augustenburg.She was a princess of Denmark through her marriage within the House of Schleswig-Holstein-Sonderburg-Glücksburg to Prince Harald of Denmark.Princess Helena was a Nazi sympathiser during World War II and was after the war exiled from Denmark, but eventually allowed to return, where she died. [SEP] Knowledge 2: Princess Karoline Mathilde of Schleswig-Holstein-Sonderburg-Glücksburg
Princess Karoline Mathilde of Schleswig- Holstein- Sonderburg- Glücksburg( Viktoria- Irene Adelheid Auguste Alberta Feodora Karoline Mathilde of Schleswig -Holstein- Sonderburg- Glücksburg; 11 May 1894 – 28 January 1972) was a member of the House of Schleswig- Holstein- Sonderburg- Glücksburg and Princess of Schleswig- Holstein- Sonderburg- Glücksburg by birth and a member of the House of Solms Baruth and Countess of Solms Baruth through her marriage to Count Hans of Solms- Baruth.
Knowledge 1: Princess Helena Adelaide of Schleswig-Holstein-Sonderburg-Glücksburg
Princess Helena Adelaide of Schleswig-Holstein-Sonderburg-Glücksburg (1 June 1888 - 30 June 1962) was the third eldest daughter of Friedrich Ferdinand, Duke of Schleswig-Holstein and his wife Princess Karoline Mathilde of Schleswig-Holstein-Sonderburg-Augustenburg.She was a princess of Denmark through her marriage within the House of Schleswig-Holstein-Sonderburg-Glücksburg to Prince Harald of Denmark.Princess Helena was a Nazi sympathiser during World War II and was after the war exiled from Denmark, but eventually allowed to return, where she died. [SEP] Knowledge 2: Friedrich Ferdinand, Duke of Schleswig-Holstein
Friedrich Ferdinand of Schleswig- Holstein- Sonderburg- Glücksburg( 12 October 1855 – 21 January 1934) was the fourth Duke of Schleswig- Holstein- Sonderburg- Glücksburg and became Duke of Schleswig- Holstein in 1931.

Answer: Frederick VIII, Duke of Schleswig-Holstein