From what I read, the English attempted to have a marriage alliance with Aragon, the later 1200's but did not happened because Aragon is on interdict, Eleanor of England, Countess of Bar was originally to marry Alfonso III of Aragon..
I think if Matilda of Brittany, the younger sister of Eleanor and Arthur of Brittany who died in Early childhood in OTL could be married off to Peter III of Aragon, Eleanor of Brittany is too prestigious to be used as an alliance and Philippe Auguste would veto that..I think if an Anglo-Aragonese alliance happens the 1190's there will be no Aragonese involvement in the Cathar crusade.
I think if Matilda of Brittany, the younger sister of Eleanor and Arthur of Brittany who died in Early childhood in OTL could be married off to Peter III of Aragon, Eleanor of Brittany is too prestigious to be used as an alliance and Philippe Auguste would veto that..I think if an Anglo-Aragonese alliance happens the 1190's there will be no Aragonese involvement in the Cathar crusade.