Princess Augusta of Saxe-Meiningen
Princess Augusta Louise Adelaide Caroline Ida of Saxe-Meiningen (6 August 1843 – 11 November 1919) was the daughter of Bernhard II, Duke of Saxe-Meiningen and his wife Princess Marie Frederica of Hesse-Kassel.
She was the mother of Ernst II, Duke of Saxe-Altenburg.
Princess Marie Luise Charlotte of Hesse-Kassel
Princess Marie Luise Charlotte of Hesse- Kassel,( 9 May 1814 – 28 July 1895) was a member of the House of Hesse- Kassel by birth.
Through her marriage to Prince Frederick Augustus of Anhalt- Dessau, she became a princess of Anhalt- Dessau.
George Charles of Hesse-Kassel
George Charles of Hesse-Kassel (8 January 1691 – 5 March 1755) was a prince of Hesse-Kassel and a Prussian General.
Charles I, Landgrave of Hesse-Kassel
Charles of Hesse- Kassel( 3 August 1654 – 23 March 1730), of the House of Hesse, was the Landgrave of Hesse- Kassel from 1670 to 1730.
Margravine Hedwig Sophie of Brandenburg
Hedwig Sophia of Brandenburg( 14 July 1623, Berlin- 26 June 1683, Schmalkalden) was Landgravine consort of Hesse- Kassel by marriage to William VI, Landgrave of Hesse- Kassel, and regent from 1663 until 1677 during the minority of her sons, William VII, Landgrave of Hesse- Kassel and Charles I, Landgrave of Hesse- Kassel.
Princess Marie Frederica of Hesse-Kassel
Princess Marie Frederica Wilhelmina of Hesse-Kassel (6 September 1804 – 1 January 1888) was a Duchess consort of Saxe-Meiningen by marriage to Bernhard II, Duke of Saxe-Meiningen.
She was the daughter of William II, Elector of Hesse and Princess Augusta of Prussia.
Prince William of Hesse-Kassel
Prince William of Hesse- Kassel( 24 December 1787 – 5 September 1867), was the first son of Prince Frederick of Hesse- Kassel and Princess Caroline of Nassau- Usingen.
Sophie Charlotte of Hesse-Kassel
Sophie Charlotte of Hesse- Kassel( 16 July 1678, Kassel – 30 May 1749, Bützow) was a princess of Hesse- Kassel and by marriage Duchess of Mecklenburg.
William VII, Landgrave of Hesse-Kassel
William VII of Hesse- Kassel( 21 June 1651 – 21 November 1670) was Landgrave of Hesse- Kassel.
Princess Augusta of Prussia
Princess Augusta of Prussia (Christine Friederike Auguste; 1 May 1780 – 19 February 1841) was a German salonist, painter, and Electress consort of Hesse by marriage to William II, Elector of Hesse.
She was the third daughter and fifth child of Frederick William II of Prussia and Frederika Louisa of Hesse-Darmstadt.

Question: Who is Princess Marie Frederica Of Hesse-Kassel's maternal grandfather?
Answer: Frederick William II of Prussia