Take this with a grain of salt of however you'd pluck out news in the internet, but via a scoop at Comic Book Movie, it looks like we may now have a fourth playable character coming to Warner Bros. Interactive and Rocksteady Studios' Batman: Arkham City, and it's none other than the first Robin and ward of Bruce Wayne, Dick Grayson aka Nightwing!
Word of Nightwing's appearance in the sequel to Batman: Arkham Asylum was speculated for some time now (and hoped by big Batfans). In website PSTrophies, the trophy list to Batman Arkham City was updated, and featured in it were specific trophies dedicated to the orphaned circus acrobat and protege of Batman. This means that like the other DLC character Tim Drake/ Robin, Dick Grayson/ Nightwing will be playable as an extra character outside of the main campaign mode, which allows players to control Batman and Catwoman in the main story.
Nightwing has yet to be officially confirmed, but there's a strong possibility now that word like this is out. You can check more on the scoop from the source posts at CBM and PSTrophies for details.
Batman Arkham City debuts on the Xbox 360 and PS3 on October 18,