The rebel barons responded by inviting the French prince Louis to lead them: Louis had a claim to the English throne by virtue of his marriage to Blanche of Castile, a granddaughter of Henry II. Philip may have provided him with private support but refused to openly support Louis, who was excommunicated by Innocent for taking part in the war against John. Louis' planned arrival in England presented a significant problem for John, as the prince would bring with him naval vessels and siege engines essential to the rebel cause. Once John contained Alexander in Scotland, he marched south to deal with the challenge of the coming invasion.