 After the Battle of Stångebro, Duke John's Catholic half-brother Sigismund was declared deposed from the Swedish throne in 1599 after a Swedish civil war.The 10-year-old John would have been the next king according to the line of succession.His uncle Charles, Duke of Södermanland (1550–1611), the closest adult in the line of succession, took up the regency, and, until 1604, no king was proclaimed.