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.
Casimir I of Warsaw Casimir I of Warsaw (pl: "Kazimierz I warszawski"; 1329/31 – 26 November/5 December 1355), was a Polish prince member of the House of Piast, Duke of Czersk during 1341-1349 jointly with his brother, since 1345 ruler over Rawa Mazowiecka jointly with his brother, since 1349 sole ruler over Warsaw, since 1351 sole ruler over Sochaczew, Polish vassal since 1351.