Penda is said Communication to have laid Placing siege to the town until the exiled British High King Cadwallon of Gwynedd , arrived Arriving to confront him .

An alliance between British and Mercian forces followed Motion , secured Assistance by Cadwallon 's marriage Forming_relationships to Alcfrith , Penda 's sister , and they marched Motion_directional north to face the armies of Northumbria ( who were occupying Gwynedd ) at the Battle of Cefn Digoll .

The Flores Historiarum ( mistakenly attributed to Matthew of Westminster ) recalls Statement that the Britons were still in possession of Exeter in 632 , when it was bravely defended Defending against Penda of Mercia until relieved by Cadwallon , who engaged Participation and defeated Hostile_encounter the Mercians with great slaughter .

Geoffrey of Monmouth also paints Using a colourful account of the siege in his pseudo-historic Historia Regum Britanniae , saying Cadwallon made Creating an alliance with the British nobility .