The engagement of Maria and Alfonso was not formalised until she was seven, but it had been reconfirmed by King Henry III's last will and testament. By the same arrangement, Maria's brother John was to marry Alfonso's sister Maria and Maria's sister Catherine was to marry Alfonso's brother Henry. The marriage of Maria and Alfonso was celebrated in the Cathedral of Valencia on 12 June 1415. The couple was wedded by Antipope Benedict XIII who had also provided a dispensation for their marriage. Maria was given a splendid dowry in form of land and revenues, while Alfonso was raised to the rank of infante of Castile. Her brother would later complain that the dowry was too large and that it was in fact the largest dowry ever given to an infanta of Castile.