Friedrich, Duke of Schleswig-Holstein-Sonderburg-Glücksburg
Friedrich of Schleswig- Holstein- Sonderburg- Glücksburg( 23 October 1814 in Schleswig, Duchy of Schleswig – 27 November 1885 in Luisenlund, Schleswig- Holstein, Prussia) was the third Duke of Schleswig- Holstein- Sonderburg- Glücksburg.
Friedrich was the second- eldest son of Friedrich Wilhelm, Duke of Schleswig- Holstein- Sonderburg- Glücksburg and Princess Louise Caroline of Hesse- Kassel and an elder brother of Christian IX of Denmark.
Friedrich inherited the title of Duke of Schleswig- Holstein- Sonderburg- Glücksburg upon his childless brother Karl's death on 14 October 1878.
Prince Harald of Denmark
Prince Harald of Denmark ("Harald Christian Frederik"; 8 October 1876 – 30 March 1949) was a member of the Danish Royal Family.
He was the third son and fourth child of Frederick VIII of Denmark and his wife, Lovisa of Sweden, and thus brother to Christian X of Denmark.
The prince served in the Royal Danish Army for most of his life, and reached the rank of Lieutenant General.
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.
Count Oluf of Rosenborg
Oluf, Count of Rosenborg
( Oluf Christian Carl Axel; 10 March 1923 – 19 December 1990), a former Danish prince, was the younger child and son of Prince Harald of Denmark by his wife, Princess Helena Adelaide of Schleswig- Holstein- Sonderburg- Glücksburg.
Prince Julius of Schleswig-Holstein-Sonderburg-Glücksburg
Prince Julius of Schleswig-Holstein- Sonderburg- Glücksburg( 14 October 1824, Gottorp, Schleswig, Duchy of Schleswig – 1 June 1903, Itzehoe, Schleswig- Holstein, Germany) was the eighth of the ten children of Friedrich Wilhelm, Duke of Schleswig- Holstein- Sonderburg- Glücksburg and Princess Louise Caroline of Hesse- Kassel.
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.
Friedrich Wilhelm, Duke of Schleswig-Holstein-Sonderburg-Glücksburg
Friedrich Wilhelm, Duke of Schleswig-Holstein-Sonderburg-Glücksburg (4 January 1785 – 17 February 1831) inherited the title of Duke of Schleswig-Holstein-Sonderburg-Beck in 1816.
He subsequently changed his title to Duke of Schleswig-Holstein-Sonderburg-Glücksburg in 1825 and founded a line that includes the Royal Houses of Denmark, Greece, Norway, and the Commonwealth realms.
Augusta of Schleswig-Holstein-Sonderburg-Glücksburg
Princess Augusta of Schleswig-Holstein- Sonderburg- Glücksburg( 27 June 1633 – 26 May 1701) was a Danish- German princess of the senior Glücksburg line of the Duke of Schleswig- Holstein.
She was the first Duchess of Augustenborg by marriage.
Augustenborg palace, and as a consequence the nearby town, were named in honor of her.
The great- granddaughter of king Christian III of Denmark, she was the third daughter, eighth by birth, of Philip, Duke of Schleswig- Holstein- Sonderburg- Glücksburg and Princess Sophia Hedwig of Saxe- Lauenburg.
She was sister of Sophia Dorothea of Schleswig- Holstein- Sonderburg- Glücksburg
Karl, Duke of Schleswig-Holstein-Sonderburg-Glücksburg
Karl of Schleswig -Holstein- Sonderburg- Glücksburg( 30 September 1813 at Gottorp in Schleswig, Duchy of Schleswig – 24 October 1878 at Luisenlund, Glücksburg, in Schleswig- Holstein, Prussia) was the second Duke of Schleswig- Holstein- Sonderburg- Glücksburg.
Karl was the eldest son of Friedrich Wilhelm, Duke of Schleswig- Holstein- Sonderburg- Glücksburg and Princess Louise Caroline of Hesse- Kassel and an elder brother of Christian IX of Denmark.
Karl became Duke of Schleswig- Holstein- Sonderburg- Glücksburg upon his father's death on 27 February 1831.
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.

Question: Who is Princess Helena Adelaide Of Schleswig-Holstein-Sonderburg-Glücksburg's father-in-law?
Answer: Frederick VIII of Denmark