According to Deadline, Rosenbaum closed a deal on Friday to appear in the series finale which will air on the CW on May 13.
“It feels like the stars are aligning, literally. We couldn’t be more excited about having Michael back,” Smallville executive producers/showrunners Kelly Souders and Brian Peterson said. “And as far as the way he returns … there’ll be no doubt about how Lex becomes the great rival in Clark Kent’s life. He is the villain of the story.”
“I’m simply doing it for all of the fans out there who made Smallville the great success it is,” Rosenbaum said. “I appreciate all of their passion, their relentlessness and even their threats. Ha ha. I can’t wait to hug the old crew back in Vancouver one last time and see all of my old friends once again….. Oh, and for Lex to become the badass he’s destined to be.”