The Krieg the Psycho DLC for Borderlands 2 will be due on 14th May, according to Krieg's official Twitter feed.
Since that's a Tuesday, this is likely referring to the North American PSN and worldwide Steam release dates. European consoles will likely get it the following day on XBL and PSN.
The expansion was priced earlier at $9.99 or 800 Microsoft Points as part of the Psycho Pack, and will not be included in the Season Pass.
The sixth Borderlands 2 class - and second available as DLC after the Necromancer - was first announced at PAX East as a "high risk/high reward" build that encourages melee "Buzz Axe" attacks and stringing together quick combos. He also inflicts extra fire damage when he himself is on fire, because that's just how Krieg rolls.
Looking ahead, Borderlands 2's fourth non-character DLC expansion, Tiny Tina's Assault on Dragon Keep, will be out on 25th June for the same price, and is the final installment to be included in the Season Pass.