Petronilla of Aquitaine (c. 1125 – 1193) was the daughter of William X of Aquitaine and Aenor of Châtellerault. She was the sister of Eleanor of Aquitaine, who was Queen consort of England. She is variously called Alix (or Aelith in Occitan) and Petronilla; she typically went by Alix after her marriage, while Petronilla seems to have been her childhood name (she is referred to as such in her father's will).
Petronilla accompanied her sister to the French court, where she met the very-married Count Raoul I of Vermandois, a cousin to her brother-in-law Louis VII of France. He repudiated his wife and married her, and they were excommunicated by the Pope. Pope Innocent II promised to lift the excommunication, but recanted his promise in 1143. Hostilities flared, and Louis VII infamously burned Vitry. Finally the Pope died and his successor Pope Celestine II lifted the excommunication at Council of Reims in 1144. However, Petronilla and Raoul divorced in 1151, as he remarried the next year. Petronilla remained a member of the French royal court and a constant companion to her sister Eleanor while she was imprisoned by her husband King Henry II in England and Wales. After Henry's death, Eleanor was freed, and Petronilla planned on returning to France. Yet, records of Petronilla after 1189 are scarce. It is believed that she came down with a fever on her voyage from England back to France and died in early 1190 before her arrival at port. Together Raoul and Petronilla had three children: