After Stephen was captured at the Battle of Lincoln in 1141, she rallied the king's partisans, and raised an army with the help of William of Ypres. While the Empress Matilda waited in London to prepare her coronation, Matilda and Stephen's brother Henry of Blois had her chased out of the city. The Empress Matilda went on to besiege Henry of Blois at Winchester. Matilda of Boulogne then commanded her army to attack the besiegers. There was a rout in which the Empress's half-brother, Robert of Gloucester, was captured. The two Matildas then agreed to exchange prisoners and Stephen ruled as king again.