Early campaigns in Scotland Between 1297 and 1298, Edward was left as regent in charge of England while the king campaigned in Flanders against Philip IV, who had occupied part of the English king's lands in Gascony. On his return, Edward I signed a peace treaty, under which he took Philip's sister, Margaret, as his wife and agreed that Prince Edward would in due course marry Philip's daughter, Isabella, who was then only two years old. In theory, this marriage would mean that the disputed Duchy of Gascony would be inherited by a descendant of both Edward and Philip, providing a possible end to the long-running tensions. The young Edward seems to have got on well with his new stepmother, who gave birth to Edward's two half-brothers, Thomas of Brotherton and Edmund of Woodstock, in 1300 and 1301. As king, Edward later provided his brothers with financial support and titles. Edward I returned to Scotland once again in 1300, and this time took his son with him, making him the commander of the rearguard at the siege of Caerlaverock Castle. In the spring of 1301, the king declared Edward the Prince of Wales, granting him the earldom of Chester and lands across North Wales; he seems to have hoped that this would help pacify the region, and that it would give his son some financial independence. Edward received homage from his Welsh subjects and then joined his father for the 1301 Scottish campaign; he took an army of around 300 soldiers north with him and captured Turnberry Castle. Prince Edward also took part in the 1303 campaign during which he besieged Brechin Castle, deploying his own siege engine in the operation. In the spring of 1304, Edward conducted negotiations with the rebel Scottish leaders on the king's behalf and, when these failed, he joined his father for the siege of Stirling Castle. In 1305, Edward and his father quarrelled, probably over the issue of money. The prince had an altercation with Bishop Walter Langton, who served as the royal treasurer, apparently over the amount of financial support Edward received from the Crown. The king defended his treasurer, and banished Prince Edward and his companions from his court, cutting off their financial support. After some negotiations involving family members and friends, the two men were reconciled. The Scottish conflict flared up once again in 1306, when Robert the Bruce killed his