 Following his victory in the Battle of Pavia, Charles abandoned the idea of an English alliance, cancelled his engagement to Mary and decided to marry Isabella and form an alliance with Portugal.He wrote to Isabella's brother, King John III of Portugal, making a double marriage contract – Charles would marry Isabella and John would marry Charles's youngest sister, Catherine.A marriage to Isabella was more beneficial for Charles, as she was closer to him in age, was fluent in Spanish and provided him with a very handsome dowry of 900,000 Portuguese cruzados or Castilian folds that would help to solve the financial problems brought on by the Italian Wars.