Arthur Gerald Wellesley, Earl of Mornington, is the great-great-grandson of what  last German Emperor ("Kaiser") and King of Prussia?
Arthur Wellesley, Earl of Mornington Arthur Gerald Wellesley, Earl of Mornington (born 31 January 1978 at St Mary's Hospital in Paddington, London) is the son of Charles Wellesley, 9th Duke of Wellington. The Wellesleys are an aristocratic Anglo-Irish family. Through his mother, Antonia von Preussen, Duchess of Wellington, he is great-great-grandson of Kaiser Wilhelm II. As a descendant of Queen Victoria, he is eligible to succeed to the British throne.
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).