The Wardens met Zazikel in Starkhaven, luring him into what was supposed to be a trap. The Archdemon had somehow been aware of the assault, and the Wardens found themselves surrounded by darkspawn instead. During the Battle of Starkhaven, Corin and his lover the Warden mage Neriah met the Archdemon head-on while fighting off a legion of darkspawn. Neriah threw herself in front of an emissary's bolt to shield him. She was slain, but Corin survived, going on to plunge his blade into the Archdemon and end the Second Blight.
See also EditCodex entry: Vestments of Sacrifice