After Gustav's death, his oldest son Eric XIV ascended the throne. His regency was marked by Sweden's entrance into the Livonian War and the Northern Seven Years' War, and the mutual relation between his developing mental disorder and the opposition with the aristocracy, leading to the Sture Murders (1567) and the imprisonment of his brother John (III), who was married to Catherine Jagiellonica, the sister of Sigismund II Augustus of Poland. A magnates' uprising led by John led to Erik's deposition and the kingship of John, followed by the regency of John's son Sigismund. Sigismund however was not able to defend the throne against Gustav's youngest son Charles (IX)