Élisabeth of France ( '' Élisabeth Philippine Marie Hélène de France '' ; 3 May 1764 -- 10 May 1794 ) , known as `` Madame '' Élisabeth , was a French princess and the youngest sibling of King Louis XVI .
Princess Élisabeth of France , `` Granddaughter of France '' ( Élisabeth Philippine Marie Hélène de France ( 3 May 1764 -- 10 May 1794 ) , known as Madame Élisabeth , was a French princess . She was the youngest sibling of King Louis XVI .