NBC might have cancelled "Constantine" after just one season but in an interview with IGN, "Arrow" co-showrunner Wendy Mericle stated that there is still a possibility for the character to pop up and crossover into "Arrow" season 4 or beyond. 

"Yeah, we really want to do it," Mericle explained. "It's something we've been talking to DC about and it's just a question of certain political things, but also the actor's schedule. We're trying to work it out, but we don't know 100 percent if it's going to happen... We're really optimistic and we would love to have him, it would be very exciting." 

This wouldn't be the first time that a crossover had been in the works. As per a report from Screen Rant, "Arrow" star Stephen Amell stated that he was interested in making an appearance in "Constantine" if it would get another season. That, of course, went nowhere since the show was canned due to financial concerns and low ratings. 

Despite "Constantine" coming from NBC and "Arrow" coming from The CW network, a crossover would still be viable since both series are produced by the Warner Bros. Television studios. This is also why "Arrow" and "The Flash" could someday crossover with "Supergirl" despite the latter being on CBS. 

As stated in a report from Blastr, it would make sense to bring John Constantine to the world of "Arrow" now that the show has established some supernatural elements in it such a Ra's al Ghul and the Lazarus Pit which can rejuvenate a person's age and bring back the dead. Constantine is, after all, a master of magic and expert on mysticism. 

Although the crossover is not yet official, it appears that the studios are pushing forward to get it done. Not only would it be a second chance for Constantine but it would also give them a chance to resolve the cliffhanger ending from "Constantine" season 1. 

"Arrow" season 4 premieres this Oct. 7.