God therfor was wroth

In late May 1265 Gilbert de Clare, Earl of Gloucester, abandoned Simon de Montfort and joined Lord Edward, lately escaped from Hereford. Clare's role in the royalist comeback, after the disaster of Lewes, should not be underrated. He was enormously powerful, with lands all over England, Wales and Ireland, almost a king in his own right.

Before joining Edward, he and his ally John Giffard took to the forests near Gloucester, from where they defied the Montfortians. Every night the pugnacious Giffard lit a fire in the woods, to let the enemy know of his location and dare them to attack. As Robert of Gloucester put it:

“The Earl of Gloucester was in the forest beside, And Sir John Giffard also upon a high hill lay; Which is called Erdland, both night and day: A great fire he made there, at nights, of wood and spray, And drew a track thereabout which was wide seen, And into Gloucester also, so that his foes might see, Where they should find him on that hill high.”

Simon's response to the desertion of Clare was to pump out yet more futile propaganda. He forced the hapless Henry III to issue a public denunciation, in which Clare was condemned as “having now fled to assist the rebellion de Warenne, in contempt of his oath to abide by the written agreement, which had lately appeased the discord between him and the Earl of Leicester”.

This referred to the agreement of 12 May, whereby Simon and Clare attempted to resolve their differences. Obviously, it had failed to do the trick. Late in the month, Clare met with Edward at Wigmore castle and extracted an oath from the prince, whereby he promised to expel all the aliens from the kingdom and abide by English laws. Knowing he could not succeed without Clare's support, Edward coughed up everything that was demanded of him.

There is little doubt that Clare was pursuing a private vendetta against Simon. Shortly after his defection, he sent men to drag Stephen de Herewell, Simon's chaplain and private secretary, from sanctuary in a church and behead him. Not everyone was impressed with Clare's policy. Robert Mannyng, a 14th century English chronicler and Gilbertine monk, wrote that the death of Clare's son, another Gilbert, at the battle of Bannockburn was God's vengeance on the father for deserting Simon:

“Schent is ilk Baroun, now Gilbert turnes grim, The Montfort Sir Simoun most affied on him. Alas, Sir Gilbert, thou turned thin oth, At Stryvelyn [Bannockburn] men it herd how God therfor was wroth”.