Johan Banér was born at Djursholm Castle in Uppland. As a four-year-old he was forced to witness how his father, the Privy Councillour Gustaf Banér, and uncle, Sten Axelsson Banér (also a Privy Councillour), were executed at the Linköping Bloodbath in 1600. They were accused of high treason by King Charles IX because of their support of King Sigismund, and though it was the father of King Gustavus Adolphus who had Banér's father executed the two men developed a strong friendship from an early age, mostly because Gustavus Adolphus reinstated the Banér family soon after his coronation.[citation needed]