 On 28 May 1271 Isabella married Philip of Sicily, son of Charles I of Sicily.This marriage had been pre-determined by the Treaty of Viterbo in May 1267 between Charles, the exiled Baldwin II of Constantinople and Isabella's father.Taking advantage of the precarious situation of the remains of the Latin Empire in the face of renascent Greek power, Charles gained suzerain rights over Achaea; furthermore, the heirs of Baldwin and William were to marry children of Charles, and Charles was to have the reversion of both the Empire and the Principality should the couples have no heirs.