It was the kingdom of Aragon, when Alfonso the Battler died without a direct heir and stated in his last will that the Knights Templars, the Hospitallers, and the Knights of the Holy Sepulchre were to inherit the kingdom. In fact, no one wanted that solution, not even the orders, who where not willing to be in charge of such a big thing.
It was was dismissed out of hand by the nobility of Aragon and possible successors were sought. In fact, the successor was his own brother, Ramiro.
Then that would be actually interesting, especially in linguistics: if ATL Aragon expanded southward as part of the Iberian Reconquista, I think they would spread an ATL Aragonese language, which was heavily influenced by Occitan, especially the Pyrenean Gascon variant, instead of OTL Aragonese where it was spread by the southern Navarrese.If the orders didn´t want to rule Aragon, then it is hard to make the ATL happen. Would be interesting to look how a government of three knightly Orders would look in Aragon.