Question: Dorothea von Salviati's father-in-law was born on what date?

full_context: Document 1: Princess Tatiana of Sayn-Wittgenstein-Berleburg: Princess Tatiana of Sayn-Wittgenstein-Berleburg (Tatiana Louise Ursula Therese Elsa; born 31 July 1940) is the fourth child and second daughter of Gustav Albrecht, 5th Prince of Sayn-Wittgenstein-Berleburg, and his wife, Margareta Fouché d'Otrante, and younger sister of Prince Richard of Sayn-Wittgenstein-Berleburg, the husband of Princess Benedikte of Denmark. Tatjana is the former wife of the late Moritz, Landgrave of Hesse, from 1980 head of the House of Hesse. Their marriage took place in the summer of 1964 in Gießen. They divorced in 1974.
Document 2: Dorothea von Salviati: Dorothea von Salviati (1907–1972), 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.
Document 3: Prince Oskar of Prussia: Prince Oskar Karl Gustav Adolf of Prussia ("Oskar Karl Gustav Adolf Prinz von Preußen"; 27 July 1888 – 27 January 1958) was the fifth son of Wilhelm II, German Emperor and Augusta Victoria of Schleswig-Holstein.
Document 4: Princess Dorothea of Saxe-Coburg and Gotha: Princess Dorothea Maria Henriette Auguste Louise of Saxe-Coburg and Gotha (30 April 1881 – 21 January 1967) was a princess of Saxe-Coburg and Gotha (German: "Prinzessin von Sachsen-Coburg und Gotha" ) by birth and the duchess of Schleswig-Holstein (German: "Herzogin zu Sachsen" ) through her marriage to Ernst Gunther, duke of Schleswig-Holstein. Dorothea was born in Vienna, Austria, the second child and only daughter of Prince Philipp of Saxe-Coburg and Gotha and Princess Louise of Belgium.
Document 5: 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.
Document 6: Princess Stephanie of Windisch-Graetz: Princess Stéphanie of Windisch-Graetz (April 4, 1909 in Ploskovice, Bohemia – May 29, 2005 in Uccle, Belgium) was the daughter of Prince Otto Weriand of Windisch-Graetz (1873–1952) and Archduchess Elisabeth Marie of Austria (1883–1963), only child of Crown Prince Rudolf of Austria and Princess Stéphanie of Belgium. She was the great-grandchild of Emperor Franz-Joseph and Empress Elisabeth ('Sissi') of Austria. She was also the great-grandchild of King Leopold II of Belgium.
Document 7: Dorothea von Medem: (Anna Charlotte) Dorothea von Medem (3 February 1761 – 20 August 1821) was born a Gräfin (Countess) of the noble German Baltic Medem family and later became Duchess of Courland (a Baltic region). Popularly known as Dorothea of Courland after her marriage to Peter von Biron, the last Duke of Courland, she hosted an aristocratic salon in Berlin and performed various diplomatic duties on behalf of her estranged husband.
Document 8: German Emperor: The German Emperor (German: Deutscher Kaiser) was the official title of the head of state and hereditary ruler of the German Empire. A specifically chosen term, it was used between the 18 January 1871 proclamation of King of Prussia and President of the North German Confederation Wilhelm I as ""Deutscher Kaiser"" and the official abdication of Wilhelm II on 28 November 1918. The Holy Roman Emperor is sometimes also called "German Emperor" when the historical context is clear, as derived from the Holy Roman Empire's official post-1512 title of "Holy Roman Empire of the German Nation."
Document 9: Princess Dorothea of Courland: Dorothea von Biron, Princess of Courland, Duchess of Dino, Talleyrand, and Sagan, known as Dorothée de Courlande or Dorothée de Dino (21 August 1793 – 19 September 1862), was a Baltic German noblewoman. Her mother was Dorothea von Medem, Duchess of Courland, and although her mother's husband, Duke Peter von Biron, acknowledged her as his own, her true father might be Polish statesman Aleksander Batowski. For a long time, she accompanied the French statesman Charles Maurice de Talleyrand-Périgord, whereas she was the separated wife of his nephew, Edmond de Talleyrand-Périgord.
Document 10: Rudolf, Crown Prince of Austria: Rudolf, Crown Prince of Austria (Rudolf Franz Karl Joseph; 21 August 1858 – 30 January 1889) was the only son of Emperor Franz Joseph I and heir apparent to the throne of Austria-Hungary from birth. In 1889, he died in a suicide pact with his mistress, Baroness Mary Vetsera, at the Mayerling hunting lodge. The ensuing scandal made international headlines. He was named after the first Habsburg King of Germany, Rudolf I, who assumed the throne in 1273.
Document 11: Wilhelm, German Crown Prince: 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.
Document 12: Prince Christian-Sigismund of Prussia: Prince Christian-Sigismund of Prussia (born March 14, 1946) is one of the three paternal uncles of Georg Friedrich, Prince of Prussia, head of the House of Hohenzollern since 1994, which reigned over Germany until 1918. He is the youngest of four sons born to Louis Ferdinand, Prince of Prussia (1907-1994) and Grand Duchess Kira Kirillovna of Russia (1909-1967). He was the heir presumptive to the headship of the deposed House of Hohenzollern from the death of his father to 20 January 2013, when Georg Friedrich fathered twin sons, relegating Christian-Sigismund to a more remote place in the Line of succession to the former German throne.
Document 13: Archduchess Margaretha of Austria: Archduchess Margaretha of Austria German: "Margaretha, Erzherzogin von Österreich-Toskana" ;(8 May 1894 – 21 January 1986) was a daughter of Archduke Leopold Salvator of Austria and Infanta Blanca of Spain. She was member of the Tuscan branch of the Imperial House of Habsburg, an Archduchess of Austria and Princess of Tuscany by birth. After the fall of the Austro Hungary Empire, she lived in exile, first in Barcelona and from the 1930s until the end of her life in Italy. In 1937, she married an Italian diplomat, Marchese Francesco Maria Taliani de Marchio. The couple, who had married in their forties, did not have children.
Document 14: Princess Amalia of Saxe-Weimar-Eisenach: Amalia Maria da Gloria Augusta (Ghent, 20 March 1830 — Walferdange, Luxembourg, 1 May 1872), Princess of Saxe-Weimar-Eisenach, was the first wife of Prince Henry of the Netherlands, son of king William II of the Netherlands.
Document 15: William I, German Emperor: William I, or in German Wilhelm I (full name: "William Frederick Louis of Hohenzollern", German: "Wilhelm Friedrich Ludwig von Hohenzollern" , 22 March 1797 – 9 March 1888), of the House of Hohenzollern was King of Prussia from 2 January 1861 and the first German Emperor from 1 January 1871 to his death, the first Head of State of a united Germany. Under the leadership of William and his Minister President Otto von Bismarck, Prussia achieved the unification of Germany and the establishment of the German Empire. Despite his long support of Otto von Bismarck as Minister President, William held strong reservations about some of Bismarck's more reactionary policies, including his anti-Catholicism and tough handling of subordinates. Contrary to the domineering Bismarck, William was described as polite, gentlemanly and, while a staunch conservative, more open to certain classical liberal ideas than his grandson Wilhelm II.
ground_truth: 6 May 1882