Tjuyu
Tjuyu( sometimes transliterated as Thuya or Thuyu) was an Egyptian noblewoman and the mother of queen Tiye, and the wife of Yuya.
She is the grandmother of Akhenaten, and great grandmother of Tutankhamun.
Hubba bint Hulail
Hubba bint Hulail was the grandmother of Hashim ibn' Abd Manaf, thus the great- great- great- grandmother of the Islamic" Nabī"( Prophet) Muhammad ibn Abdullah.
Princess Elisabeth of Prussia
Princess Elisabeth of Prussia( 18 June 1815 – 21 March 1885) was the second daughter of Prince Wilhelm of Prussia and Landgravine Marie Anna of Hesse- Homburg and a granddaughter of Frederick William II of Prussia.
Prince Philip, Duke of Edinburgh is her great- great- grandson.
Mona Hopton Bell
Mona Hopton Bell( 1867- 1940) was a British artist, best known for her portraits of civic figures.
She was the grandmother of the painter Jean H. Bell.
Princess Charlotte of Prussia (1831–1855)
Princess Charlotte of Prussia( 21 June 1831 – 30 March 1855), was by birth a Princess of Prussia and member of the House of Hohenzollern and by marriage Hereditary Princess of Saxe- Meiningen.
She was the eldest child and daughter of Prince Albert of Prussia( younger son of Frederick William III of Prussia and Louise of Mecklenburg- Strelitz) and his first wife Princess Marianne of the Netherlands( daughter of William I of the Netherlands and Wilhelmine of Prussia).
Prince Christian-Sigismund of Prussia
Prince Christian-Sigismund of Prussia (born March 14, 1946) is one of the three paternal uncles of Georg Friedrich, Prince of Prussia, head of the House of Hohenzollern since 1994, which reigned over Germany until 1918.
He is the youngest of four sons born to Louis Ferdinand, Prince of Prussia (1907-1994) and Grand Duchess Kira Kirillovna of Russia (1909-1967).
He was the heir presumptive to the headship of the deposed House of Hohenzollern from the death of his father to 20 January 2013, when Georg Friedrich fathered twin sons, relegating Christian-Sigismund to a more remote place in the Line of succession to the former German throne.
Prince Friedrich Sigismund of Prussia (1891–1927)
Prince Joachim Viktor Wilhelm Leopold Friedrich Sigismund of Prussia( 17 December 1891 – 6 July 1927) was a German World
War I fighter pilot and member of the House of Hohenzollern.
He was the son of Prince Friedrich Leopold of Prussia and Princess Louise Sophie of Schleswig- Holstein- Sonderburg- Augustenburg, married in 1916.
Hannah Arnold
Hannah Arnold, also known as Hannah Waterman King, was the grandmother of Benedict Arnolds children.
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.
Grand Duchess Kira Kirillovna of Russia
Grand Duchess Kira Kirillovna of Russia (9 May 1909 – 8 September 1967) was the second daughter of Grand Duke Kirill Vladimirovich of Russia and Princess Victoria Melita of Saxe-Coburg and Gotha.
She married the head of the German Imperial House, Prince Louis Ferdinand of Prussia.

Question: Who is Prince Christian-Sigismund Of Prussia's maternal grandmother?
Answer: Princess Victoria Melita of Saxe-Coburg and Gotha