A new photo book, with an introduction by James Gunn, offers a behind-the-scenes look at the making of the new Superman, out this July.

“It was just difficult to figure out where I was going to come from with Superman ,” Gunn said speaking to io9 in Los Angeles last week. “And I think that it really started with my dog in a lot of ways. The idea of putting in Krypto, I think, was the fun part for me, because that was something that we hadn’t really seen in a Superman movie.”

In fact, the idea of Lex Luthor and the Joker teaming up is the subject of the classic animated movie The Batman/Superman Movie: World's Finest, which marks the first crossover between Superman: The Animated Series and Batman: The Animated Series all the way back in 1997.

So it kind of goes without saying that David Corenswet, Rachel Brosnahan, and Nicholas Hoult will be back after the events of Superman, in theaters July 11. But if you ask them about it, they aren’t so sure.