[2][3] His surname is derived from a vowel shift in pronunciation of d'Allemagne ("of Germany"); he was so called by the elites of England because of his father's status as the elected German King of Almayne.

[6] As a nephew of both Henry III and Simon de Montfort, he wavered between the two at the beginning of the Barons' War, but finally took the royalist side and was among the hostages taken by Montfort after the Battle of Lewes (1264), was held at Wallingford Castle and later released.

[7][8] In 1268 he took the cross with his cousin Edward, who, however, sent him back from Sicily to pacify the unruly province of Gascony.

[9] While attending mass at the church of San Silvestro (also called the Chiesa del Gesù) in Viterbo on 13 March 1271, Henry was murdered by his cousins Guy and Simon de Montfort the Younger, sons of Simon de Montfort, 6th Earl of Leicester, in revenge for the beheading of their father and older brother at the Battle of Evesham.

[10] The deed is mentioned by Dante Alighieri, who took it upon himself to place Guy de Montfort in the seventh circle of hell in his masterpiece, The Divine Comedy,[9] which was written at least 40 years after Henry's death.