Pascent, Paschent, Passent
The third son of Vortigern and brother of Vortimer, Catigern, and Faustus.
Nennius mentions that after his father’s death, he was granted the rule of Buelt and Gwerthrynion by the new king, Ambrosius Aurelius.
Geoffrey, however, contends that Pascentius fled to Germany, raised an army, and returned to Britain to attack Ambrosius. After one defeat, he allied with King Gilloman of Ireland and tried again. He sent a Saxon assassin named Eopa to kill Ambrosius in the guise of a doctor, gave him a poisoned drink from which he died. Uther and his army met Pascentius and Gilloman near St. David’s (or at Menevia) and killed them.
Wace says that Pascentius hated his father because of his father’s dealings with the Saxons. Thomas Heywood erroneously makes him a Saxon.
Sources
The Life of Merlin | Thomas Heywood, 1641
Brut | Layamon, late 12th century to mid-13th century
Historia Regum Britanniae | Geoffrey of Monmouth, c. 1138
Historia Brittonum | Probably Nennius, early 9th century
Roman de Brut | Wace, c. 1155