Geoffrey of Monmouth (Penguin Classics ed. p. 131) says "When Coel, King of the Britons, heard of the coming of Constantius,..". Camalodunum is a Roman name. Where do you find the Welsh geneologies, mentioning Coel? I don't have such and haven't even been able to find any of Rachel Bromwich's works. Cuel is mentioned (barely) in 'Culwych and Olwen', but what he was wasn't mentioned, except most, in the long list of notables there, were warriors.