They've decided, to give us a sixth vault hunter.
The preview showed us that he will more than likely be a melee focused character, much like Brick in the first Borderlands. Looks to be some kind of creature. It also featured this quote;
"Deep beneath Pandora, an experiment has escaped. Bandits beware, a new Vault Hunter is coming. More mayhem awaits."Matt Armstrong, Franchise Director for Gearbox, told Joystiq this;
“DLC is announced on a very tight schedule, and I don’t think you’ll have to wait long until you see that character.”
I'm extremely keen to get my hands on this, and I'm sure you are too. Just know, this DLC character won't be part of your season pass, you'll have to fork out for this one.