Simon de Montfort knights Gilbert de Clare and his brother Thomas two days later, on May 14, just before the Battle of Lewes.

Montfort is still in control of London, as Henry regains control over Kent and Sussex.

Montfort marches out of London to negotiate, but the terms—involving maintaining the provisions —are rejected by the king.

The only option remaining is to fight.

Gilbert de Clare commands the central division of the baronial army, which forms up on the Downs west of Lewes.

When Prince Edward leaves the field in pursuit of Montfort's routed left wing, the King and Richard of Cornwall, Henry's brother and the titular king of Germany, are thrown back to the town.

Henry takes refuge in the Priory of St. Pancras, and Gilbert accepts the surrender of the Earl of Cornwall, who had hidden in a windmill.

In spite of inferior numbers, the baronial force have won a spectacular victory, capturing the king, Lord Edward, and the Earl of Cornwall.

Montfort and de Clare are now supreme and de Montfort in effect de facto King of England.