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.
Prince Leopold of Bavaria Leopold Maximilian Joseph Maria Arnulf, Prinz von Bayern (9 February 1846 – 28 September 1930) was born in Munich, the son of Prince Regent Luitpold of Bavaria (1821–1912) and his wife Archduchess Augusta of Austria (1825–1864). He was a Field Marshal ("Generalfeldmarschall") who commanded German and Austro-Hungarian forces on the Eastern Front in World War I.