In what year did Sigismund Casimir's mother die?
Cecilia Renata of Austria Archduchess Cecilia Renata of Austria (German: "Cäcilia Renata"; Polish: "Cecylia Renata"; 16 July 1611 – 24 March 1644) was Queen of Poland as consort to the Polish-Lithuanian Commonwealth's King Władysław IV Vasa.
Countess Maria of Nassau (1556–1616) Countess Maria of Nassau (7 February 1556, Breda – 10 October 1616, Buren) was the second daughter of William the Silent by his first wife Anna of Egmond and Buren. She was named after William's first daughter, Maria, who had died in infancy.