Henry of Almain was born on November 2, 1235, the only surviving child of Richard of Cornwall and Isabel Marshal, making him the only direct descendent of both King John and William Marshal. In 1257, his father was crowned King of Germany and knighted Henry at the coronation ceremony in Aachen. Thereafter, Henry was known as “of Almain” to indicate he was the crown prince of Germany (Allemagne). He returned to England, where he was the eldest of the Plantagenet cousins at court. They included Edward, the heir to the throne, and the sons of Simon de Montfort, whose mother Eleanor was Richard of Cornwall’s youngest sister. In 1260, they left together to tourney in France.

The next year Edward suddenly cut off his former companions. They sought revenge against him and the royal family by encouraging Simon to wage war against Henry III. Simon returned in 1263, and in a lightning offensive, forced the king to again submit his rule to a baronial council led by Simon. Most likely at Simon’s insistence, Henry of Almain pursued a hated royal adviser to Flanders but was captured and imprisoned. After the king secured his release, Almain returned and reconciled Edward to his former companions, including himself. Back again on the royal side, he went to Simon to apologize for deserting him, assuring him he would never fight against him, but Simon merely laughed and told his nephew he was of no importance in any account.  

War broke out again in 1264 and Henry of Almain was captured along with most of the royal family at Lewes. He was released by Simon to seek recognition for the revolutionary Montfortian government and was still on the continent when Edward escaped, raised an army, and defeated and killed Simon at Evesham. Almain returned and led royalist forces in their most significant defeat of Montfortians in the War of the Disinherited, but also helped bring the war to an end to by negotiating the Dictum of Kenilworth. In 1269 he married Constance, the daughter of Simon’s mortal enemy Gaston de Bearn. The next year he left with Edward and other knights to join the crusade of Louis IX in Africa, but Louis was dead by the time they got there.

Edward continued on to the Holy Land but Almain accompanied Charles of Anjou, King of Sicily, and the new king of France, Philip III, to Italy. They stopped in Viterbo, where the college of cardinals was at an impasse over electing a new pope. Almain was there to remind the cardinals that whoever was named pope had an obligation to crown his father Richard as the Holy Roman Emperor. Edward asked him to seek reconciliation with their Montfort cousins, two of whom had risen high in service to Charles of Anjou. On this day of March 13th in 1271, Almain was attending mass in a small church next to his lodgings when Guy and Simon de Montfort the younger burst in and hacked him to death at the altar. They then dragged his corpse outside and mutilated it in the fashion of the mutilation wrought on their father’s body at Evesham. Almain had not been at Evesham, but the Montforts wanted revenge and he was a convenient target. He was 35 and had no children.

Richard of Cornwall and his sister Eleanor de Montfort remained on good terms after her husband’s death. What if any word passed between them following the murder of his son by her sons is unknown. Henry of Almain was brought home to England by his brother Edmund and buried at the altar of Hailes Abbey, which was built by Richard. It became the family crypt, but centuries later was destroyed by marauding Tudors. The marauding Montforts escaped justice for his murder, although Guy de Montfort was later captured in war and died in prison after Edward blocked efforts to release him.