According to TVline.com, their is a new clue about who's returning to Smallville. We know Martha Kent is coming back, so this leads me to believe that the answer is Curtis Knox.
Question: I’ve been going crazy with your Smallville Blind Item and finally have a guess that I haven’t seen here on any other sites: Saturn Girl! Am I right? Mejia
Ausiello: Nope. The answer is ****** K***.