According the the totally unreliable Geoffrey of Monmouth, who gives the only history of King Coel of Colchester (Penguin edition, p. 132), Coel died before his Daughter Helen married Constantius. Their son, Constantine, went to Rome. 'He captured the city and then was made overlord of the whole world'. Three of Helen's uncle subsequently appear, and were made Roman senators. I don't remember that from Gibbon's 'Decline and Fall...'.