Question: Who is Prince Sigismund Of Prussia (1896–1978)'s maternal grandfather?

Knowledge 1: Prince Sigismund of Prussia (1896–1978)
Prince William Victor Charles Augustus Henry Sigismund of Prussia (27 November 1896 at Kiel – 14 November 1978 at Esparza, Costa Rica), was the second son of Prince Henry of Prussia and his wife, Princess Irene of Hesse and by Rhine.He was a nephew of Kaiser Wilhelm II and Tsarina Alexandra of Russia.A great-grandson of Queen Victoria through both his parents, he was the only one of three brothers who did not have the hemophilia common among her descendants. [SEP] Knowledge 2: Princess Irene of Hesse and by Rhine
Princess Irene of Hesse and by Rhine ("Irene Luise Marie Anne, Princess of Hesse and by Rhine", 11 July 1866 – 11 November 1953) was the third child and third daughter of Princess Alice of the United Kingdom and Louis IV, Grand Duke of Hesse and by Rhine.Her maternal grandparents were Queen Victoria and Prince Albert of Saxe-Coburg and Gotha.Her paternal grandparents were Prince Charles of Hesse and by Rhine and Princess Elizabeth of Prussia.She was the wife of Prince Henry of Prussia, a younger brother of Wilhelm II, German Emperor and her first cousin.The SS "Prinzessin Irene", a liner of the North German Lloyd was named after her.Her siblings included Princess Victoria of Hesse and by Rhine, wife of Prince Louis of Battenberg, Grand Duchess Elizabeth Feodorovna of Russia, wife of Grand Duke Sergei Alexandrovich of Russia, Ernest Louis, Grand Duke of Hesse and by Rhine, and Empress Alexandra Feodorovna of Russia, wife of Tsar Nicholas II of Russia.Like her younger sister, the empress, Irene was a carrier of the hemophilia gene, and Irene would lose her sisters Alix and Elisabeth in Russia to the Bolsheviks.
Knowledge 1: Princess Irene of Hesse and by Rhine
Princess Irene of Hesse and by Rhine ("Irene Luise Marie Anne, Princess of Hesse and by Rhine", 11 July 1866 – 11 November 1953) was the third child and third daughter of Princess Alice of the United Kingdom and Louis IV, Grand Duke of Hesse and by Rhine.Her maternal grandparents were Queen Victoria and Prince Albert of Saxe-Coburg and Gotha.Her paternal grandparents were Prince Charles of Hesse and by Rhine and Princess Elizabeth of Prussia.She was the wife of Prince Henry of Prussia, a younger brother of Wilhelm II, German Emperor and her first cousin.The SS "Prinzessin Irene", a liner of the North German Lloyd was named after her.Her siblings included Princess Victoria of Hesse and by Rhine, wife of Prince Louis of Battenberg, Grand Duchess Elizabeth Feodorovna of Russia, wife of Grand Duke Sergei Alexandrovich of Russia, Ernest Louis, Grand Duke of Hesse and by Rhine, and Empress Alexandra Feodorovna of Russia, wife of Tsar Nicholas II of Russia.Like her younger sister, the empress, Irene was a carrier of the hemophilia gene, and Irene would lose her sisters Alix and Elisabeth in Russia to the Bolsheviks. [SEP] Knowledge 2: Princess Calixta of Lippe
Princess "Calixta" Agnes Adelaide Irmgard Helene Caroline Elise Emma of Lippe (14 October 1895 - 15 December 1982) was the wife of Prince Waldemar of Prussia, eldest son of Prince Henry of Prussia.
Knowledge 1: Princess Irene of Hesse and by Rhine
Princess Irene of Hesse and by Rhine ("Irene Luise Marie Anne, Princess of Hesse and by Rhine", 11 July 1866 – 11 November 1953) was the third child and third daughter of Princess Alice of the United Kingdom and Louis IV, Grand Duke of Hesse and by Rhine.Her maternal grandparents were Queen Victoria and Prince Albert of Saxe-Coburg and Gotha.Her paternal grandparents were Prince Charles of Hesse and by Rhine and Princess Elizabeth of Prussia.She was the wife of Prince Henry of Prussia, a younger brother of Wilhelm II, German Emperor and her first cousin.The SS "Prinzessin Irene", a liner of the North German Lloyd was named after her.Her siblings included Princess Victoria of Hesse and by Rhine, wife of Prince Louis of Battenberg, Grand Duchess Elizabeth Feodorovna of Russia, wife of Grand Duke Sergei Alexandrovich of Russia, Ernest Louis, Grand Duke of Hesse and by Rhine, and Empress Alexandra Feodorovna of Russia, wife of Tsar Nicholas II of Russia.Like her younger sister, the empress, Irene was a carrier of the hemophilia gene, and Irene would lose her sisters Alix and Elisabeth in Russia to the Bolsheviks. [SEP] Knowledge 2: Princess Barbara of Prussia
Princess Barbara of Prussia (2 August 192031 May 1994) was the only daughter and elder child of Prince Sigismund of Prussia and Princess Charlotte of Saxe-Altenburg.She was a great-granddaughter of Frederick III, German Emperor and a great-great-granddaughter of Queen Victoria.On 17 September 1952 she was legally adopted by her paternal grandmother, Princess Irene of Prussia ("née" Princess Irene of Hesse and by Rhine), a granddaughter of Queen Victoria.

Answer: Louis IV, Grand Duke of Hesse