Ambrosius Aurelianus
Arthur was first styled as a king of the Britons in Geoffrey of Monmouth's pseudo-historical chronicle "Historia Regum Britanniae" ("History of the Kings of Britain"), which dates to c. 1136. Geoffrey also refers to Ambrosius Aurelianus (whom he calls Aurelius Ambrosius) as a king of Britain and an older brother of Uther Pendragon, father of Arthur, thus establishing a familial relationship between Aurelianus and Arthur. He identifies Aurelius Ambrosius as the son of Constantinus, a Breton ruler and brother of .