Question: Who is Prince Hubertus Of Prussia's maternal grandfather?

Knowledge 1: 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. [SEP] Knowledge 2: 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.
Knowledge 1: 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. [SEP] Knowledge 2: 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.
Knowledge 1: 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. [SEP] Knowledge 2: 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.

Answer: Frederick Francis III, Grand Duke of Mecklenburg-Schwerin