Michael C. Hall plays a crime-solving serial killer on the hit show Dexter, while Jennifer Carpenter co-stars as his detective sister with a Daddy complex. But the on-set siblings share an even closer bond when the cameras are off: The pair are dating, sources have told People.

“I don’t see what the big deal is,” said a source close to the couple. “They play brother and sister on the show, but they are actors, after all.”

Hall and Carpenter were spotted dining out in Los Angeles recently.

“It was romantic,” an observer said. “They were drinking champagne and there was the clinking of glasses.”