Áed Dub mac Suibni (died c. 588) was an Irish king of the Dál nAraidi in the over-kingdom of Ulaid (in modern Ulster).
The Annals of Tigernach report, more prosaically, that Diarmaid was killed by Áed Dub in 565 at Ráith Bec, on the plain of Mag Line (Moylinny, near Larne), in the lands of the Dál nAraidi.
He writes that when Columba learned of this, he prophesied that although Áed would live for many years to come, he "will return as a dog to his vomit; he will again be a bloody murderer and in the end, killed by a spear, he will fall from wood into water and die drowning."
Adomnán says that this priest, Findchán loved Áed Dub in a worldly or corrupt way - carnaliter amans.
From Adomnán's account it can be surmised that Áed was deposed, or abdicated, and spent time in Britain in a monastery before, presumably, returning to Ulster to try to regain his throne.