Ernest Augustus I of Hanover ( 5 June 1771 â `` 18 November 1851 ) was the fifth son and eighth child of George III of the United Kingdom . Ernest Augustus I ( 5 June 1771 â `` 18 November 1851 ) was King of Hanover from 20 June 1837 until his death . He was the fifth son and eighth child of George III , who reigned in both the United Kingdom and Hanover .