However, there existed a rival claim to the principality in the person of Matilda of Hainaut, the wife of Guy II de la Roche, Duke of Athens.
As part of a series of marriages and pacts that year, Philip made a second marriage to Catherine of Valois, titular Latin Empress (who had been betrothed to Louis' brother, Hugh V of Burgundy), while Charles was betrothed to his new stepmother's sister, Joan of Valois in compensation for the breaking off of his previous engagement.
In 1315, Philip went north in command of Neapolitan troops to relieve the Florentine Guelphs, besieged at Montecatini by the Pisan Ghibellines under Uguccione della Faggiuola.
Despite initial successes, Philip fell ill with fever, and was crushingly defeated by Uguccione at the Battle of Montecatini.
Rainieri della Gherardesca had sworn not to be knighted until he had been revenged on the Angevins for the death of his father, who had been executed by Charles I of Naples with Conradin in 1268.