Longtime Arrowverse producer and writer Marc Guggenheim has confirmed yet another DC adaptation is linked to The CW’s five-part Crisis on Infinite Earths mega-event: HBO’s currently airing Watchmen series. A blink-and-you’ll-miss-it reference to the show was seen in Tuesday’s episode of The Flash, which served as a midway point for the crossover before a brief break for the holidays which sees the final two parts airing in January 2020.

The franchise-merging crossover, based on the classic comic event from 1985, has been jam-packed with many DC Comics easter eggs and return appearances, ranging from ones which were known ahead of time (like both Tom Welling and Brandon Routh reprising their roles as Clark Kent/Superman and Kevin Conroy finally portraying a live-action Bruce Wayne after voicing the character for decades) to complete surprises no one saw coming, such as Robert Wuhl returning as Alexander Knox from the 1989 Batman film or Tom Ellis appearing as Lucifer Morningstar (of Netflix’s Lucifer) after having denied rumors of doing so. But one thing fans weren’t expecting was a reference to Watchmen, given how detached Allen Moore’s influential graphic novel and the adaptions of it typically are from the mainstream DC Universe, New 52-based crossover Doomsday Clock aside.

During the third episode of the Crisis event, John Constantine, John Diggle, and Mia Smoak journey to Earth-666 in order to find Lucifer, who can help them get into Purgatory to retrieve Oliver Queen’s soul. This comes as the team’s effort to revive the fallen Green Arrow with a Lazarus Pit left him a mindless shell of his former self, and Lucifer grants them a card to access to the world of souls after hinting at some past history with Constantine. In an opening shot establishing this Earth, a billboard advertising Watchmen can be seen on the streets of Los Angeles. One eagle-eyed viewer took note of this on her Twitter page, and Guggenheim confirmed it was meant as a shout-out to the show. “Finally. Someone noticed,” he said in his response. “Special thanks to [Watchmen Executive Producer] Damon Lindelof for making this one happen.”

This isn’t the first time a fellow DC show was referenced in Lucifer’s world, as a similar billboard promoting Supergirl was seen during the show proper. Just like Watchmen, Lucifer airs on a network separate from The CW, making its involvement with the Crisis on Infinite Earths crossover event equally as surprising, however brief it was.

So far, the television adaptation of the fabled Crisis has given viewers plenty of surprising references to things they wouldn’t expect to be mentioned on The CW, such as a brief shot of Robin and Hawk from DC Universe’s Titans, or Helena Kyle from the short-lived 2002 Birds Of Prey TV show making a short return. The appearance of HBO’s Watchmen is another one of such surprises, giving viewers in the know a nice wink and nod to another part of the DC Multiverse, even if it’s little more than a two-second picture in the background. There will no doubt be more of these little nods to other works when the Arrowverse’s Crisis on Infinite Earths returns to the air on January 14.

More: Crisis On Infinite Earths Massive Cliffhanger Ending Explained

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