Question: Princess Marie of Hanover was the youngest daughter of the only successor of which German king?
Context: Princess Marie of Hanover (German: "Marie Ernestine Josephine Adolphine Henrietta Theresa Elizabeth Alexandrina Prinzessin von Hannover und Cumberland" ; 2 December 1849 – 4 June 1904) was the younger daughter of King George V of Hanover and of his wife, Princess Marie of Saxe-Altenburg. George V (George Frederick Alexander Charles Ernest Augustus; German: "Georg Friedrich Alexander Karl Ernst August" ; 27 May 1819 – 12 June 1878) was the last king of Hanover, the only child and successor of King Ernest Augustus.  George V's reign was ended by the Unification of Germany. Princess Marie of Liechtenstein ("née" Princess Marie Isabelle Marguerite Anne Geneviève of Orléans; born Boulogne-Billancourt, France on 3 January 1959) is the eldest daughter of Prince Henri, Count of Paris, Duke of France and his former wife Duchess Marie Thérèse of Württemberg.  She is the wife of Prince Gundakar of Liechtenstein, a great-grandson of Prince Alfred of Liechtenstein. Princess Olga of Hanover and Cumberland (German: "Olga Adelaide Louise Marie Alexandrina Agnes Prinzessin von Hannover und Cumberland" ; 11 July 1884 – 21 September 1958) was the youngest daughter of Ernest Augustus, Crown Prince of Hanover (1845–1923) and Princess Thyra of Denmark (1853–1933), the youngest daughter of Christian IX of Denmark (1818–1906) and Louise of Hesse-Kassel (1817–1898).  Olga was a great-great-granddaughter of George III of the United Kingdom (1738–1820) and Charlotte of Mecklenburg-Strelitz (1744–1818). Princess Marie of Hohenzollern-Sigmaringen, later Princess Marie of Belgium, Countess of Flanders (Marie Luise Alexandrine Karoline; 17 November 1845 – 26 November 1912) was a Princess of Hohenzollern-Sigmaringen, later simply of Hohenzollern, and mother of King Albert I of Belgium. Princess Marie Louise of Hanover and Cumberland (11 October 1879 – 31 January 1948) was the eldest daughter of Ernest Augustus, Crown Prince of Hanover (1845–1923) and Princess Thyra of Denmark (1853–1933), the youngest daughter of Christian IX of Denmark (1818–1906) and Louise of Hesse-Kassel (1817–1898).  Through her father, Marie Louise was a great-great-granddaughter of George III of the United Kingdom (1738–1820) and Charlotte of Mecklenburg-Strelitz (1744–1818). 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 Marie Amelie of Baden (Marie Amelie Elisabeth Caroline; 11 October 1817 – 17 October 1888) was the youngest daughter of Charles, Grand Duke of Baden and Stéphanie de Beauharnais.  In 1843, she married the Scottish nobleman William Hamilton, Marquess of Douglas and Clydesdale.  They became the Duke and Duchess of Hamilton upon the death of William's father in 1852.  Their only daughter Mary married the future Albert I, Prince of Monaco and was the mother of Louis II. Lady Mary Victoria Douglas-Hamilton, also known as the Lady Mary Victoria Hamilton (11 December 185014 May 1922) was the Lanarkshire-born, Scottish great-grandmother of Prince Rainier III of Monaco, the fashion designer Prince Egon von Fürstenberg, the socialite and actress Princess Ira von Fürstenberg and the Czech Minister of Foreign Affairs Prince Karel Schwarzenberg.  She was the daughter of William Alexander Anthony Archibald Hamilton, 11th Duke of Hamilton and of his wife, Princess Marie Amelie Elizabeth Caroline of Baden.  Through her maternal grandmother, she was a third cousin of Emperor Napoléon III of France.  She was a first cousin of Queen Carola of Saxony, Queen Stephanie of Portugal, King Carol I of Romania, and Princess Marie, Countess of Flanders (mother of King Albert I of the Belgians). Princess Marie Alexandra of Schleswig-Holstein-Sonderburg-Glücksburg, since 1941 of Schleswig-Holstein (Marie Alexandra Caroline-Mathilde Viktoria Irene; 9 July 1927, Schloss Louisenlund, Schleswig, Schleswig-Holstein, Germany – 14 December 2000, Friedrichshafen, Baden-Württemberg, Germany) was a member of the House of Schleswig-Holstein-Sonderburg-Glücksburg.  Marie Alexandra was the fourth and youngest child of Wilhelm Friedrich, Duke of Schleswig-Holstein and his wife Princess Marie Melita of Hohenlohe-Langenburg.  Her older brother Peter was the Duke of Schleswig-Holstein and Head of the House of Oldenburg from 10 February 1965 until his death on 30 September 1980.
Answer: King Ernest Augustus