 When Montfort returned to England in 1263 to begin a rebellion against King Henry III that became known as the Second Barons' War, Robert had to take sides, and moved towards Montfort.He is on record during May and June as taking the 'Three Castles'—Grosmont, Skenfrith, and Whitecastle in South Wales, which belonged to Prince Edward.When in January 1264, Louis IX of France declared the Provisions of Oxford unlawful and invalid, further unrest followed.