 His father's open support for Afonso V of Portugal in his claim to the Castilian throne made him an enemy of Ferdinand and Isabella I of Castile, and he was convicted of high treason and beheaded around 1480, after a long imprisonment.At the age of 20, Sancho avenged the memory of his father by riding to Burgos and stabbing (or, according to some records, mutilating) the judge who had sentenced him to death.He subsequently fled to Portugal, where he was well received by Afonso's successor, king John II.