The War of Saint-Sardos, a short conflict between Edward and the Kingdom of France, led indirectly to Edward's overthrow. The French monarchy used the jurisdiction of the Parlement of Paris to overrule decisions of the nobility's courts. As a French vassal, Edward felt this encroachment in Gascony with the French kings adjudicating disputes between him and his French subjects. Without confrontation he could do little but watch the duchy shrink. Edmund of Woodstock, 1st Earl of Kent, decided to resist one such judgement in Saint-Sardos with the result that Charles IV declared the duchy forfeit. Charles's sister, Queen Isabella, was sent to negotiate and agreed to a treaty that required Edward to pay homage in France to Charles. Edward resigned Aquitaine and Ponthieu to his son, Prince Edward, who travelled to France to give homage in his stead. With the English heir in her power, Isabella refused to return to England unless Edward II dismissed his favourites and also formed a relationship with Roger Mortimer, 1st Earl of March. The couple invaded England and, joined by Henry, 3rd Earl of Lancaster, captured the king. Edward II abdicated on the condition that his son would inherit the throne rather than Mortimer. He is generally believed to have been murdered at Berkeley Castle by having a red-hot poker thrust into his bowels. In 1330 a coup by Edward III ended four years of control by Isabella and Mortimer. Mortimer was executed, but although removed from power, Isabella was treated well, living in luxury for the next 27 years.