'Arrow' season 4 episode 5 spoilers & recap: executive producer sheds light on surprise 'Constantine' appearance

Earlier this year, the Daniel Cerone executive produced "Constantine," which aired on NBC was canceled after just 13 episodes of its debut season. Deadline reported that Warner Bros. TV, who produces the show, tried to market it to other networks, including The CW and Fox, but to no avail.

Cerone wrote in his letter to fans, "To leave such a significant, dedicated and active fan base on the table — that’s the real sadness. You all deserve many years of the series we set out to make, and we’re disappointed that we couldn’t deliver that to you. The good news is that Constantine will live on for years in many more forms."

Such form Cerone mentioned comes in a crossover with The CW's "Arrow," as John Constantine himself, played by Matt Ryan, made an appearance in this week's episode. Constantine was written into the story in order to help Sara Lance's (Caity Lotz) gain back her soul upon her resurrection from the Lazarus Pit. What viewers did not expect was that the Arrow had already met Constantine during his stint on the island of Lian Yu.

Arrow executive producer Wendy Mericle told The Hollywood Reporter, "We wanted to explore the idea of magic and Oliver's experience with magic in the past, and so the flashbacks became centered around Constantine."

Mericle explained that while the idea of a flashback came late in their brainstorming sessions, "We wanted to explain how they knew each other in the present-day story and suddenly it made a lot of sense, given that in the flashbacks, we always intended for Baron Reiter (Jimmy Akingbola) to be pursuing an agenda, the one that [Oliver and Constantine] prevented."

Constantine apparently used his magic on Oliver Queen, thus the mysterious tattoo that came with a promise that it will be of use in the future. Constantine's appearance on the show may be small, but meaningful throughout the course of this season, Mericle said.

The executive producer explained, "The outcome of that spell will come out later in the season. Constantine gives Oliver insurance against Baron Reiter. We will be true to that statement: that's exactly what that spell is. It will come to Oliver at a crucial point when he's extremely vulnerable and it will get him out of a really dark place."

While fans may expect Constantine to be a constant presence in Arrow moving forward, Arrow executive producer Marc Guggenheim tells USA Today that his appearance was designed to be a one-time deal.

However, Guggenheim recognizes the passion of Constantine fans, saying that the crossover was "not so much about what it does for Arrow — it’s really what it does for the fans of [Constantine]...I’m just thrilled to see him back on the small screen again."

Arrow airs every Wednesday at 8 p.m. on The CW.