Warning: The following contains SPOILERS for Crisis on Infinite Earths: Part 3

The third chapter of Crisis on Infinite Earths confirmed that Lucifer is part of the Arrowverse. Appropriately enough, the world where the series was set was officially designated as Earth-666. Despite being based on a long-running comic book series published by DC Comics' adult imprint Vertigo Comics, there was some question as to whether or not Lucifer might play a part in the long-awaited crossover event.

Early rumors suggested that actor Tom Ellis had been seen on the set where Crisis on Infinite Earths was being filmed in Vancouver, yet Ellis denied being part of the event. Of course, one of Lucifer's titles is The Prince of Lies and it seems now that Ellis may have been living up to his character's reputation. Ellis' lie is understandable, however, when one considers that the reasons for Lucifer being brought into Crisis on Infinite Earths would have spoiled too much of the main story had his presence been announced earlier.

Related: Crisis On Infinite Earths Arrives At Flash’s Death - But It’s Not As Expected

The first part of Crisis on Infinite Earths saw Oliver Queen sacrificing himself to allow more people to escape Earth-38. This led his friends to seek out a Lazarus Pit to resurrect him in the second part of Crisis. While they were successful in restoring Oliver Queen's body, only a magical ritual could restore Oliver Queen's soul but the interference of all the anti-matter leaking into the universe left John Constantine unable to complete the spell. Luckily, as usual, Constantine knew someone who owed him a favor who might be able to help: Lucifer. This right away confirmed that Lucifer - yet another DC TV show - exists in the Arrowverse.

John Constantine Matt Ryan and Lucifer Tom Ellis

The Flash season 6, episode 9, "Crisis on Infinite Earths: Part 3" saw Constantine travel to Los Angeles on Earth-666 along with Oliver's best friend, John Diggle, and his daughter, Mia Smoak. It was here that he confronted Lucifer outside a familiar looking night club and told him that he was calling in his favor. After using his powers to get Mia to confess her heart's deepest desire ("I desire to get my father back."), Lucifer agreed to help because he still owed Constantine for some prior incident involving Mazikeen. To that end, he gave John a tarot card of The Devil which could be used to open a portal into the portion of Purgatory where Oliver Queen's soul had gone when he died.

The scene is a brief but humorous one, sure to please those fans who have been hoping for a crossover between Lucifer and Constantine for some time. There's even a nod to the comic readers, where Lucifer intentionally annoys Constantine by pronouncing his last name Constan-Tyne rather than Constan-Teen. The joke is that while the Arrowverse series have John using the Constant-Teen pronunciation, the comic book version of everyone's favorite Hellblazer pronounces his last name Constan-Tyne.

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