Dorothea von Salviati
Dorothea von Salviati( 10 September 1907–7 May 1972) was the wife of Prince Wilhelm of Prussia, the eldest son of Crown Prince Wilhelm, the eldest son and heir of the last German Emperor, Wilhelm II.
Born Dorothea von Salviati in Bonn, Nordrhein- Westfalen, on 10 September 1907, her parents were Alexander Hermann Heinrich August von Salviati and Helene" Ella" Crasemann( of the well- established Hamburg merchant family, Crasemann).
Her maternal grandfather was the famous Hamburg parliamentarian Gustav August Rudolph Crasemann.
Prince Friedrich Wilhelm of Prussia
Prince Friedrich Wilhelm of Prussia( 12 July 18809 March 1925) was a member of the House of Hohenzollern, great- grandson of Frederick William III 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.
Prince Wilhelm of Prussia (1906–1940)
Prince Wilhelm of Prussia (Wilhelm Friedrich Franz Joseph Christian Olaf; 4 July 1906 – 26 May 1940) was the eldest child of Crown Prince Wilhelm of Germany and Duchess Cecilie of Mecklenburg-Schwerin.
At his birth, he was second in line to the German throne and was expected to succeed to the throne after the deaths of his paternal grandfather and father.
Both of whom, however, outlived him.
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.
Prince Frederick of Prussia (1911–1966)
Prince Frederick of Prussia( 19 December 1911 – 20 April 1966), also known as" Mr. Friedrich von Preussen" in the United Kingdom, was the fourth son of Crown Prince Wilhelm of Germany and Duchess Cecilie of Mecklenburg- Schwerin.
Prince Alexander Ferdinand of Prussia
Prince Alexander of Prussia (Alexander Ferdinand Albrecht Achilles Wilhelm Joseph Viktor Karl Feodor; 26 December 1912 – 12 June 1985) was the only son of Prince August Wilhelm of Prussia and his wife Princess Alexandra Victoria of Schleswig-Holstein-Sonderburg-Glücksburg.
Prince Wilhelm of Hesse-Philippsthal-Barchfeld
Prince Wilhelm of Hesse(" Wilhelm Ernst Alexis Hermann"; 1 March 1905 – 30 April 1942) was German soldier and heir to the headship of the Hesse- Philippsthal line of the House of Hesse.
As a member of the House of Hesse he was styled" His Highness Prince Wilhelm of Hesse".
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.
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.

Question: Who is Prince Wilhelm Of Prussia (1906–1940)'s maternal grandfather?
Answer: Frederick Francis III, Grand Duke of Mecklenburg-Schwerin