In what year did Sigismund Casimir's mother die?
Sigismund Casimir Sigismund Casimir, Crown Prince of Poland (Polish: "Zygmunt Kazimierz Waza" ), (1 April 1640 – 9 August 1647) - was the only legitimate son of King Władysław IV and his first wife Queen Cecilia Renata. He was named after his grandfather Sigismund III, and uncle John Casimir.
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.