Alexandrine of Mecklenburg-Schwerin (24 December 1879 – 28 December 1952) was Queen of Denmark as the spouse of King Christian X.
 She was also Queen of Iceland from 1 December 1918 to 17 June 1944.
Duchess Anastasia Alexandrine Cecile Marie Luise Wilhelmine of Mecklenburg-Schwerin (Full German name: "Anastasia Alexandrine Cecile Marie Luise Wilhelmine Herzogin zu Mecklenburg-Schwerin"), (11 November 1923, Gelbensande, Free State of Mecklenburg-Schwerin, Weimar Republic – 25 January 1979, Hamburg, West Germany).
 Anastasia was the youngest child and youngest daughter of Frederick Francis IV, Grand Duke of Mecklenburg-Schwerin and his wife Princess Alexandra of Hanover and Cumberland.
Princess Elisabeth of Denmark, {'1': ", '2': ", '3': 'RE', '4': "} ("Elisabeth Caroline-Mathilde Alexandrine Helena Olga Thyra Feodora Estrid Margrethe Désirée"; born 8 May 1935 in Copenhagen) is the daughter of Hereditary Prince Knud and Hereditary Princess Caroline-Mathilde of Denmark, and is a first cousin of the present Danish monarch, Queen Margrethe II.
Duchess Marie of Mecklenburg-Schwerin (later Grand Duchess Maria Pavlovna of Russia, known as "Miechen" or "Maria Pavlovna the Elder"; 14 May 1854 – 6 September 1920) was born Marie Alexandrine Elisabeth Eleonore of Mecklenburg-Schwerin, daughter of Grand Duke Frederick Francis II of Mecklenburg-Schwerin and Princess Augusta of Reuss-Köstritz.
 A prominent hostess in St Petersburg following her marriage to the Grand Duke Vladimir Alexandrovich of Russia, she was known as the "grandest of the grand duchesses" and had an open rivalry with her sister-in-law the Empress Maria Feodorovna.
Princess Alexandrine Irene of Prussia (7 April 1915 – 2 October 1980) was the eldest daughter and fifth child of Wilhelm, German Crown Prince, and Cecile of Mecklenburg-Schwerin.
 Her grandparents were Wilhelm II, German Emperor and his wife Augusta Victoria of Schleswig-Holstein, and Frederick Francis III of Mecklenburg-Schwerin and Grand Duchess Anastasia Mikhailovna of Russia.
 Alexandrine was a member of the House of Hohenzollern.
Knud, Hereditary Prince of Denmark (Knud Christian Frederik Michael; 27 July 1900 – 14 June 1976), was the younger son and child of Christian X and Alexandrine of Mecklenburg-Schwerin.
The Danish Act of Succession, adopted on 27 March 1953, restricts the throne to those descended from Christian X and his wife, Alexandrine of Mecklenburg-Schwerin, through approved marriages.
 Succession is governed by absolute primogeniture.
Duchess Marie Louise of Mecklenburg-Schwerin (German: "Herzogin Marie Luise Friederike Alexandrine Elisabeth Charlotte Catherine Mecklenburg-Schwerin" ; 31 March 180326 October 1862) was daughter of Frederick Louis, Hereditary Grand Duke of Mecklenburg-Schwerin and consort of Georg, Duke of Saxe-Altenburg.
Frederick Augustus II (16 November 1852 in Oldenburg – 24 February 1931 in Rastede) was the last ruling Grand Duke of Oldenburg.
 He married Princess Elisabeth Anna of Prussia, daughter of Princess Maria Anna of Anhalt-Dessau and Prince Frederick Charles of Prussia.
 After her death, he married Elisabeth Alexandrine of Mecklenburg-Schwerin.
Princess Elisabeth Helene of Thurn and Taxis (German: "Elisabeth Helene, Prinzessin von Thurn und Taxis" ) (15 December 1903, Regensburg, Kingdom of Bavaria – 22 October 1976, Munich, Bavaria, Germany) was a Princess of Thurn and Taxis by birth and a Princess and Duchess of Saxony, Margravine of Meissen, and titular Queen consort of Saxony through her marriage to Friedrich Christian, Margrave of Meissen.
 Elisabeth was the sixth child of Albert, 8th Prince of Thurn and Taxis and his wife Archduchess Margarethe Klementine of Austria.

Question: Which son of Christian X and Alexandrine of Mecklenburg-Schwerin was the father of Princess Elisabeth of Denmark?
Answer: Knud, Hereditary Prince of Denmark