Complex sentence: Catherine Jagiellonica of Poland, (1526-1583), was youngest daughter of Sigismund I of Poland and Bona Sforza, mother of Sigismund I of Sweden and wife of John III of Sweden.
Split into simpler sentences: Catherine Jagiellonica of Poland, (1526-1583), was the youngest daughter of Sigismund I of Poland and Bona Sforza. She was the mother of Sigismund I of Sweden and wife of John III of Sweden.