The Flores Historiarum, attributed incorrectly to Matthew of Westminster, states that the Britons were still in possession of Exeter in 632, when it was bravely defended against Penda of Mercia until relieved by Cadwallon, who engaged and defeated the Mercians with "great slaughter to their troops".
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Geoffrey of Monmouth also details an account of the siege in his pseudo-historic Historia Brittonum, stating that Cadwallon made an alliance with the British nobility.
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Clemen ap Bledric is thought to have been king when the Britons fought the Battle of Beandun (possibly Bindon near Axmouth in east Devon) in 614.