Hereward's birth is conventionally dated as 1035/36 because the "Gesta Herewardi" says that he was first exiled in 1054 in his 18th year. However, since the account in the "Gesta" of the early part of his exile (in Scotland, Cornwall and Ireland) contains fantastic elements, it is hard to know if it is trustworthy. Peter Rex, in his 2005 biography of Hereward, points out that the campaigns in which he is reported to have fought in the region of Flanders seem to have begun around 1063 and suggests that, if he "was" 18 at the time of his exile, he was born in 1044/45. But this would be based on the assumption that the early part of the story is largely fictitious.