 It is possible that Beorhtwulf is the same person as the Beorhtwulf who witnessed a charter of Wiglaf 's in 836 . If so , this is Beorhtwulf 's first appearance in the historical record . His accession to the throne of Mercia is usually thought to have occurred in about 840 . The date is not given directly in any of the primary sources , but it is known from regnal lists that he succeeded Wiglaf as king . Historian D. P. Kirby suggests that Wiglaf 's death occurred in 839 , basing this date on the known chronology of the reigns of Beorhtwulf and Burgred , the next two Mercian kings . It is possible that Wigmund , the son of Wiglaf , was king briefly between Wiglaf and Beorhtwulf . The evidence for this possibility comes only from a later tradition concerning Wigmund 's son , Wigstan , so it is uncertain whether he actually did so . 
