WI: Isabella I of Castille married Afonso V of Portugal

Ferdinand presses his claim as a male heir, perhaps championing/wedding La Beltraneja himself if at all possible?

The Castillian-Portuguese union would presumably ally with Navarra to weaken Aragón, encouraging a Franco-Aragonese alliance in turn.
 
According to the show Isabel (which is actually reasonably historically accurate), Joanna of Portugal (mother of La Bertreneja) arranged this marriage between her brother and Isabel to sideline her, so her daughter would get the throne.
 
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