On the 24th of April, 1345, Edward determined no longer to allow Phillip to continue to benefit by his constant violations of the truce, and accordingly sent a defiance to the King of France.

De Montford, who had just succeeded in escaping from his prison in Paris, arrived at this moment in England, and shortly afterwards set sail with a small army under the command of the Earl of Northampton for Britanny, while the Earl of Derby took his departure with a larger force for the defence of Guienne.

King Edward set about raising a large army, which he determined to lead himself, but before passing over to France he desired to strengthen his hold of Flanders. The constant intrigues of Phillip there had exercised a great effect. The count of that country was already strongly in his interest, and it was only the influence of Jacob van Artevelde which maintained the alliance with England. This man had, by his talent and energy, gained an immense influence over his countrymen; but his commanding position and ability had naturally excited the envy and hatred of many of his fellow citizens, among whom was the dean of the weavers of Ghent, one Gerard Denis. The weavers were the most powerful body in this city, and had always been noted for their turbulence and faction; and on a Monday in the month of May, 1345, a great battle took place in the market-place between them and the fullers, of whom 1500 were slain. This victory of the weavers strengthened the power of the party hostile to Artevelde and the English connection; and the former saw that unless he could induce his countrymen to take some irretrievable step in favour of England they would ultimately fall back into the arms of France. Accordingly he invited Edward to pass over with a strong force into Flanders, where he would persuade the Flemings to make the Prince of Wales their duke. King Edward at once accepted the offer, and sailing from Sandwich on the 3d of July arrived in safety at Sluys. His intention had been kept a profound secret, and his arrival created the greatest surprise throughout Flanders. He did not disembark, but received on board a ship with great honour and magnificence the burgomasters of the various towns who appeared to welcome him. The king had brought with him the Prince of Wales, now fifteen years old, who wore a suit of black armour, and was therefore called "the Black Prince."