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.
Union of Krewo In a strict sense, the Union of Krewo or Act of Krėva (also Union of Krevo, Act of Kreva) was a set of prenuptial promises made in the Kreva Castle on 14 August 1385 by Jogaila, Grand Duke of Lithuania, in exchange for marriage to the underage reigning Queen Jadwiga of Poland. The act was very limited in scope and in the historiography the term "Union of Krewo" often refers not only to the particular document but to the events of 1385–1386 as a whole. After the negotiations in 1385, Jogaila converted to Christianity, married Jadwiga, and was crowned King of Poland in 1386. The union was a decisive moment in the histories of Poland and Lithuania; it marked a beginning of the four centuries of shared history between the two nations. By 1569 the Polish–Lithuanian union grew into a new state, the Polish–Lithuanian Commonwealth, and lasted until the Third Partition in 1795.