Born about 580, the son of Bledric ap Custennin, Clemen ruled after his father was killed by King Æthelfrith of Northumbria at the Battle of Bangor-is-Coed (Bangor-on-Dee, Powys Fadog) in about 613.
He married the daughter of Guitoli ap Urbgen, who was possibly a great grandson of the late king Gerren Llyngesic, and they had one known son, Petroc Baladrddellt (“Splintered Spear”) - although, according to the Welsh Bonedd y Saint (Genealogies of the Saints), Clemen was the father of St Petroc, other authorities state that this saint lived around a century earlier, the princely son of King Glywys of Glywysing,[1] making it likely Clemen was actually the father of Petroc Baladrddellt.
[4] Clemen was probably king when the Britons fought the Battle of Beandun (sometimes thought to be Bindon near Axmouth in Devon[5] but more likely to be in Somerset given the location of the earlier (577) victory at the Battle of Deorham) in 614 when, the Anglo-Saxon Chronicle tells us, King Cynegils and his son Cwichelm of Wessex invaded Dumnonia.
However, very little seems to change as the Anglo Saxon Chronicle records in 652 Cenwalth fighting at Bradford Upon Avon against an unknown foe very likely to be the Britons.
[10][11] Today's reputable historians do not mention this siege at all, considering it together with the rest of Historia Regum Britanniae as one of Geoffrey of Monmouth's many colourful inventions.