Frederick III (German: "Friedrich" ; 18 October 1831 – 15 June 1888) was German Emperor and King of Prussia for ninety-nine days in 1888, the Year of the Three Emperors.
 Friedrich Wilhelm Nikolaus Karl, known informally as "Fritz", was the only son of Emperor Wilhelm I and was raised in his family's tradition of military service.
 Although celebrated as a young man for his leadership and successes during the Second Schleswig, Austro-Prussian and Franco-Prussian wars, he nevertheless professed a hatred of warfare and was praised by friends and enemies alike for his humane conduct.
 Following the unification of Germany in 1871 his father, then King of Prussia, became the German Emperor.
 Upon Wilhelm's death at the age of ninety on 9 March 1888, the thrones passed to Frederick, who had by then been German Crown Prince for seventeen years and Crown Prince of Prussia for twenty-seven years.
 Frederick was suffering from cancer of the larynx when he died on 15 June 1888, aged fifty-six, following unsuccessful medical treatments for his condition.
The Army Group Rupprecht of Bavaria or Army Group A (German: "Heeresgruppe Kronprinz Rupprecht von Bayern") was an Army Group of the German Army, which operated on the Western Front under command of Rupprecht, Crown Prince of Bavaria , between 28 August 1916 and 11 November 1918 during World War I.
 It was formed from the short-lived Army Group Gallwitz under Max von Gallwitz (19 July - 28 August 1916).
The Army Group German Crown Prince or Army Group B (German: "Heeresgruppe Deutscher Kronprinz") was an Army Group of the German Army, which operated on the Western Front under command of Wilhelm, German Crown Prince, between 1 August 1915 and 11 November 1918 during World War I.
Army Group Centre (German: "Heeresgruppe Mitte" ) was the name of two distinct German strategic army groups that fought on the Eastern Front in World War II.
 The first Army Group Centre was created on 22 June 1941, as one of three German Army formations assigned to the invasion of the Soviet Union (Operation Barbarossa).
 On 25 January 1945, after it was encircled in the Königsberg pocket, Army Group Centre was renamed Army Group North ("Heeresgruppe Nord"), and Army Group A ("Heeresgruppe A") became Army Group Centre.
 The latter formation retained its name until the end of the war in Europe.
Army Group Courland (German: "Heeresgruppe Kurland" ) was a German Army Group on the Eastern Front which was created from remnants of the Army Group North, isolated in the Courland Peninsula by the advancing Soviet Army forces during the 1944 Baltic Offensive of the Second World War.
 The army group remained isolated until the end of World War II in Europe.
 All units of the Army Group were ordered to surrender by the capitulated Wehrmacht command on 8 May 1945.
Herzogin Cecilie was a German-built four-mast barque (windjammer), named after German Crown Princess Duchess Cecilie of Mecklenburg-Schwerin (1886–1954), spouse of Crown Prince Wilhelm of Prussia (1882–1951) ("Herzogin" being German for Duchess).
 She sailed under German, French and Finnish flags.
Muqrin bin Abdulaziz Al Saud (Arabic: مقرن بن عبدالعزيز آل سعود‎ ‎ ; born 15 September 1945) is a member of House of Saud who served as Crown Prince of Saudi Arabia from January to April 2015.
 He was Director General of Al Mukhabarat Al A'amah (Saudi Intelligence Agency) from 2005 to 2012.
 In July 2012, Muqrin was appointed King Abdullah's Advisor and Special Envoy with the rank of minister.
 On 1 February 2013, King Abdullah named him as Second Deputy Prime Minister, being the fifth Saudi royal to hold this position.
 This post was previously held by King Fahd, King Abdullah, Crown Prince Sultan, and Crown Prince Nayef.
 On 27 March 2014, he was named Deputy Crown Prince making him second in the line of succession behind his brother Salman bin Abdulaziz Al Saud.
 On 23 January 2015, upon King Abdullah's death and the accession of King Salman, Muqrin became Crown Prince and First Deputy Prime Minister.
 On 29 April 2015, King Salman replaced Prince Muqrin with Prince Muhammad bin Nayef as Crown Prince.
Princess Alexandrine Irene of Prussia (7 April 1915 – 2 October 1980) was the eldest daughter and fifth child of Wilhelm, German Crown Prince, and Cecile of Mecklenburg-Schwerin.
 Her grandparents were Wilhelm II, German Emperor and his wife Augusta Victoria of Schleswig-Holstein, and Frederick Francis III of Mecklenburg-Schwerin and Grand Duchess Anastasia Mikhailovna of Russia.
 Alexandrine was a member of the House of Hohenzollern.
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.
Wilhelm, German Crown Prince (German: "Kronprinz Wilhelm von Preußen" ; 6 May 1882 – 20 July 1951) , full name Friedrich Wilhelm Victor August Ernst, was the eldest child of the future German Emperor Wilhelm II and his wife Empress Augusta Victoria, and the last Crown Prince of the German Empire and the Kingdom of Prussia.
 After the death of his grandfather Emperor Frederick III, Wilhelm became crown prince at the age of six, retaining that title for more than 30 years until the fall of the empire on 5 November 1918.
 During World War I, he commanded the 5th Army from 1914 to 1916 and was commander of Army Group German Crown Prince for the remainder of the war.
 Crown Prince Wilhelm became Head of the House of Hohenzollern on 4 June 1941 following the death of his father and held the position until his own death on 20 July 1951.

Question: What Army Group was under the command of Wilhelm, German Crown Prince?
Answer: Army Group B