 While Amaury was not in Viterbo, and was not involved in the murder, Edward swore vengeance upon all of Simon de Montfort's sons, Amaury included.Simon the younger died that year, reportedly of a tertian fever, while Guy managed to appeal to the pope (with the aid of his father-in-law), resulting in his return to the church.In 1275, after the death of his mother at Montargis Abbey, Amaury, by then a Papal Chaplain, accompanied his younger sister Eleanor de Montfort on a winter sea voyage to Wales and her new husband, Llywelyn ap Gruffudd (the grandson of Llywelyn Fawr).