Who is Guy de Montfort from The Reckoning and what is their importance?

Guy de Montfort is the son of Simon de Montfort and Vicar of Florence. He fights with his father in the battle of Evesham, and blames his brother Bran for the battle's failure. Like Bran, he is haunted by images and ghosts of that battle, and when his cousin Hal appears in Italy, he is overcome by the desire to kill him. Henry of Almain, called Hal, is the son of King Richard and first cousin to the de Montforts and King Edward. Hal once supports Simon de Montfort in the rebellion, but then changes loyalty to King Edward. Hal is not at the battle of Evesham, but Guy cannot forgive Hal's betrayal of his father. Guy kills Hal publicly in a church and flees with his powerful father-in-law, the Count of Sovana and Pitigliano.