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.
Maximilian of Hesse-Kassel
Maximilian of Hesse- Kassel( 28 May 1689 – 8 May 1753) was a prince of Hesse- Kassel and a Generalfeldzeugmeister, Generalfeldmarschall and finally Reichsgeneralfeldmarschall in the army of the Holy Roman Empire.
Thyra von Westernhagen
Thyra, Princess Heinrich of Hanover( née Thyra von Westernhagen; born 14 August 1973) is a German forester and landowner.
As the wife of Prince Heinrich of Hanover, she is a princess of the House of Hanover.
Prince Heinrich of Hesse-Kassel
Prince Heinrich Wilhelm Konstantin Viktor Franz of Hesse-Kassel
(English:
Henry William Constantine Victor Francis of Hesse-Kassel, Italian:
Enrico d'Assia; 30 October 1927 – 18 November 1999) was a member of the House of Hesse.
Prince Heinrich was born in Rome, Italy, the son of Landgrave and Prince Philipp of Hesse and Princess Mafalda of Savoy, daughter of King Victor Emmanuel III of Italy.
During the Second World War, Heinrich's father was arrested by the Gestapo and his mother was detained and imprisoned in Buchenwald concentration camp, where she was killed by Allies' bombardments in 1944.
Heinrich and his siblings (Moritz, Otto and Elisabeth) were given sanctuary in the Vatican.
After the war they were reunited with their father in Germany.
Heinrich was an artist and set designer, active mainly in Italy under the name Enrico d'Assia.
He published a volume of memoirs, "Der Kristallene Lüster" (Munich, 1994).
He died in Frankfurt, unmarried.
Princess Mafalda of Savoy
Princess Mafalda of Savoy (2 November 1902 – 27 August 1944) was the second daughter of King Victor Emmanuel III of Italy and his wife Elena of Montenegro.
The future King Umberto II of Italy was her younger brother.
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.
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.
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.
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.

Question: Who is Prince Heinrich Of Hesse-Kassel's maternal grandmother?
Answer: Elena of Montenegro