Eleanor de Montfort [SEP] father
Eleanor de Montfort, Princess of Wales
Eleanor de Montfort, Princess of Wales and Lady of Snowdon (1252 – 19 June 1282) was an English noble. She was the daughter of Simon de Montfort, 6th Earl of Leicester and Eleanor of England. She was also the second woman who can be shown to have used the title Princess of Wales.
Early life.
Eleanor's maternal grandparents were John of England and his queen consort Isabella of Angoulême. 
Her maternal uncles included Henry III of England and Richard
Edward's cousin, by virtue of his father, Henry III being the elder brother of both Eleanor of England and Henry of Almain's father, Richard, Earl of Cornwall).
Henry, whom the de Montfort sons considered a traitor to their father's ideals, was attacked during mass at Viterbo, and murdered on the altar steps, resulting in the excommunication of both de Montfort sons. While Amaury was not in Viterbo, and was not involved in the murder, Edward swore vengeance upon all of Simon de Montfort