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.
Francis II, Holy Roman Emperor Francis II (German: "Franz" ; 12 February 1768 – 2 March 1835) was the last Holy Roman Emperor, ruling from 1792 until 6 August 1806, when he dissolved the Holy Roman Empire of the German Nation after the decisive defeat at the hands of the First French Empire led by Napoleon at the Battle of Austerlitz. In 1804, he had founded the Austrian Empire and became Francis I, the first Emperor of Austria, ruling from 1804 to 1835, so later he was named the one and only "Doppelkaiser" (double emperor) in history.