Arthur Gerald Wellesley, Earl of Mornington, is the great-great-grandson of what  last German Emperor ("Kaiser") and King of Prussia?
Wilhelm II, German Emperor Wilhelm II or William II (German: "Friedrich Wilhelm Viktor Albert von Preußen", English: Frederick William Victor Albert of Prussia; 27 January 18594 June 1941) was the last German Emperor ("Kaiser") and King of Prussia, ruling the German Empire and the Kingdom of Prussia from 15 June 1888 to 9 November 1918. He was the eldest grandchild of the British Queen Victoria and related to many monarchs and princes of Europe.
Frederick, Prince of Hohenzollern Frederick, Prince of Hohenzollern (German: "Friedrich Viktor Pius Alexander Leopold Karl Theodor Ferdinand Fürst von Hohenzollern" ) (30 August 1891 in Heiligendamm, Mecklenburg-Schwerin – 6 February 1965 in Krauchenwies, Baden-Württemberg, Germany) was the eldest son of William, Prince of Hohenzollern and Princess Maria Teresa of Bourbon-Two Sicilies. He had a twin brother, Franz Joseph, Prince of Hohenzollern-Emden, who was born a few minutes after he was.