Josce 's grandson Fulk fitzWarin , who died in 1258 , is ostensibly the hero of a lost romantic poem called Fouke le Fitz Waryn . The work survive as French prose in a loose corpus of medieval literature known as the Matter of England . However , it appear to confuse events of Fulk fitzWarin 's lifetime with those of his grandfather 's . Other errors in the work include transposing some of the Welsh Marcher barons of King Henry I of England 's reign into nobles of William the Conqueror 's time , and omitting an entire generation of fitzWarins . Although scholars believe Fouke le Fitz Waryn draw on genuine tradition , the difficulty in separating the fitzWarin biographies make it a problematic source .