If Ferdinand of Aragon predeceases his father and did not have a son - Aragon might pass to Francis Phoebus of Foix, I was thinking of a marriage between Francis Phoebus of Navarre and Joanna of Castille, since her theoretical husband, Duke of Guyenne had died already, a Bearn-Navarre - Aragon - Castille union interests me, is it possible?