Supernatural fans that packed Hall H at Comic-Con today weren't the only ones shocked by a spoiler dropped by producer Sera Gamble.

After hearing that "Jo is coming back," stars Jensen Ackles and Jared Padelecki turned to their boss and said: "Really?"

Yes, really, explained Gamble: "That's the perfect example of someone who died and, when we were looking at the dailes, I said, 'I can't wait to bring her back."

Other tidbits revealed at the panel:

• Chuck Shurley will not return.
• Episode three will delve into Sam's past.
• At one point, a fan mentioned that a church group had called Castiel the "antichrist." In response, Misha Collins hinted at a storyline: "I don't know how they figured that out because I tried really hard to keep that under wraps. That's kind of ironic. You'll understand when you see the first episode of the season."

And that first episode will air on September 23.

Matt Richenthal is the Editor in Chief of TV Fanatic. Follow him on Twitter and on Google+.