Charles IV ( November 11 , 1748 - January 20 , 1819 ) was King of Spain from December 14 , 1788 until his abdication on March 19 , 1808 . Charles IV ( Carlos Antonio Pascual Francisco Javier Juan Nepomuceno Jose Januario Serafin Diego ; 11 November 1748 -- 20 January 1819 ) was King of Spain from 14 December 1788 until his abdication on 19 March 1808 .