 Æthelberht was put to death by Offa of Mercia under unclear circumstances ; the site of his murder was apparently the royal vill at Sutton Walls . According to the Anglo @-@ Saxon Chronicle , he was beheaded . Mediaeval sources tell how he was taken captive whilst visiting his future Mercian bride Ælfthyth and was then murdered and buried . In Richard of Cirencester 's account of the murder , which cannot be substantiated , Offa 's evil queen Cynethryth poisoned her husband 's mind until he agreed to have his guest killed . Æthelberht was then bound and beheaded by a certain Grimbert and his body was unceremoniously disposed of . The mediaeval historian John Brompton 's Chronicon describes how the king 's detached head fell off a cart into a ditch where it was found , before it restored a blind man 's sight . According to the Chronicon , Ælfthyth subsequently became a recluse at Crowland and her remorseful father founded monasteries , gave land to the Church and travelled on a pilgrimage to Rome . 
