 Lancaster ’ s main ally was Guy Beauchamp , Earl of Warwick . Warwick was the most fervently and consistently antagonistic of the earls , and remained so until his early death in 1315 . Other earls were more amenable . Gilbert de Clare , Earl of Gloucester , was Gaveston ’ s brother @-@ in @-@ law and stayed loyal to the king . Aymer de Valence , Earl of Pembroke , would later be one of the king ’ s most central supporters , yet at this point he found the most prudent course of action was to go along with the reformers . Of the barons , at least Robert Clifford and William Marshall seemed to have royalist leanings . 
