There were some medieval Anglo-Iberian ties of substance in OTL (Black Prince fighting in Castille, and Anglo-Portuguese alliance), but nothing like the mutual back and forth of invasions and attempted conquests like between France and England from 1066 to the mid-1500s.
How could we have a noble in Spain (Leon, Castile, Navarre, or a predecessor kingdom) having some theoretical claim to the english throne and conquer England? Could feudal ties somehow entangle England in an equivalent of the “100 years war” Leon, or Castille?