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 Augustus I of Saxony Frederick Augustus I (full name: "Frederick Augustus Joseph Maria Anthony John Nepomuk Aloysius Xavier"; German: "Friedrich August Josef Maria Anton Johann Nepomuk Alois Xavier" ; Polish: "Fryderyk August Józef Maria Antoni Jan Nepomucen Alojzy Ksawery Wettyn" ; 23 December 1750 – 5 May 1827) was King of Saxony (1805–1827) from the House of Wettin. He was also Elector Frederick Augustus III ("Friedrich August III.") of Saxony (1763–1806) and Duke Frederick Augustus I (Polish: "Fryderyk August I" ) of Warsaw (1807–1813).