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 Hubertus of Hohenlohe-Langenburg
Prince Hubertus of Hohenlohe- Langenburg( born 2 February 1959 in Mexico City as Hubertus Rudolph zu Hohenlohe- Langenburg) is a Mexican Alpine skier, photographer, businessman, and a pop singer known as Andy Himalaya and Royal Disaster.
He belongs to a family which reigned over a principality in what is now the northeastern of Baden- Württemberg in Germany until the early 19th century.
Princess Marianne of Prussia
Princess Marianne of Prussia( 23 August 19131 March 1983) was a member of the House of Hohenzollern, daughter of Prince Friedrich Wilhelm of Prussia.
Duchess Cecilie of Mecklenburg-Schwerin
Duchess Cecilie of Mecklenburg-Schwerin (Cecilie Auguste Marie; 20 September 1886 – 6 May 1954) was the last German Crown Princess and Crown Princess of Prussia as the wife of German Crown Prince Wilhelm, the son of German Emperor Wilhelm II.
Cecilie was a daughter of Frederick Francis III, Grand Duke of Mecklenburg-Schwerin and Grand Duchess Anastasia Mikhailovna of Russia.
She was brought up with simplicity and her early life was peripatetic, spending summers in Mecklenburg and the rest of the year in the south of France.
After the death of her father, she traveled every summer between 1898 and 1904 to her mother's native Russia.
On 6 June 1905, she married German Crown Prince Wilhelm.
The couple had four sons and two daughters.
Cecile, tall and statuesque, became popular in Germany for her sense of style.
However, her husband was a womanizer and the marriage was unhappy.
After the fall of the German monarchy, at the end of World War I, Cecile and her husband lived mostly apart.
During the Weimar Republic and the Nazi period, Cecilie lived a private life mainly at Cecilienhof Palace in Potsdam.
With the advance of the Soviet troops, she left the Cecilienhof in February 1945, never to return.
She settled in Bad Kissingen until 1952 when she moved to an apartment in the Frauenkopf district of Stuttgart.
In 1952, she published a book of memoirs.
She died two years later.
Princess Magdalena Reuss of Köstritz
Princess Magdalena Reuss of Köstritz (20 August 1920 - 10 October 2009) was the wife of Prince Hubertus of Prussia.
She was a member of the House of Reuss.
Prince Hubertus of Hohenzollern
Prince Hubertus of Hohenzollern( Hubertus Gustav Adolf Veit Georg Meinrad Maria Alexander)( born 10 June 1966) is the third child of Prince Johann Georg of Hohenzollern and of his wife Princess Birgitta of Sweden, sister of King Carl XVI Gustaf of Sweden.
Hubertus was born in Munich, Germany.
Princess Marie of Prussia (1855–1888)
Princess Marie of Prussia(" Marie Elisabeth Louise Frederika"; 14 September 1855, Marmorpalais, Potsdam – 20 June 1888, Dresden), was a princess of the House of Hohenzollern.
She was the daughter of Prince Frederick Charles of Prussia and later became second wife of Prince Henry of the Netherlands then the first wife of Prince Albert of Saxe- Altenburg.
She was also the great- niece of Wilhelm I, German Emperor.
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.
Prince Hubertus of Prussia
Prince Hubertus of Prussia (Hubertus Karl Wilhelm; 30 September 1909 – 8 April 1950) was the third son of Crown Prince Wilhelm of Germany and Duchess Cecilie of Mecklenburg-Schwerin.
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.

Question: Who is Prince Hubertus Of Prussia's maternal grandfather?
Answer: Frederick Francis III, Grand Duke of Mecklenburg-Schwerin