premise: Wolfgang Mozart had only daughters.
hypothesis: Maria Constanze Cäcilia Josepha Johanna Aloysia Mozart ( née Weber ) ( 5 January 1762 -- 6 March 1842 ) was the wife of Wolfgang Amadeus Mozart . Franz Xaver Wolfgang Mozart ( 26 July 1791 -- 29 July 1844 ) , also known as Wolfgang Amadeus Mozart , Jr. , was the youngest child of six born to Wolfgang Amadeus Mozart and his wife Constanze . He was the younger of his parents ' two surviving children .