Complex sentence: There is however a theory that Eléonore could be a daughter of Raoul and his second wife Petronilla of Aquitaine, who was a daughter of William X of Aquitaine and Aenor of Châtellerault.
Split into simpler sentences: There is however a theory considering that Eléonore could instead be a daughter of Raoul and his second wife Petronilla of Aquitaine. Petronilla was a daughter of William X of Aquitaine and Aenor of Châtellerault.