the praetorian praefect, and the son-in-law of the emperor Numerian, murdered the emperor, as it was said, on the retreat of the army from Persia to the Hellespont. He carefully concealed the death of Numerian, and issued all the orders in his name, till the soldiers learnt the truth by breaking into the imperial tent on the Hellespont. They then elected Diocletian as his successor, A. D. 284, who straightway put Aper to death with his own hand without any trial. Vopiscus relates that Diocletian did this to fulfil a prophecy which had been delivered to him by a female Druid, " Imperator eris, cum Aprum occideris." (Vopisc. Numer. 12-14; Aurel. Vict. de Caes. 38, 39, Epit. 38; Eutrop. 9.12, 13.)
A Dictionary of Greek and Roman biography and mythology
Smith, William
A Dictionary of Greek and Roman biography and mythology. William Smith, LLD, ed. 1890