A recent social media posting from the writers of Legends of Tomorrow revealed the revival of a classic augmented reality Easter egg from the short-lived Constantine series. The revival coincides with the upcoming guest appearance of Constantine star Matt Ryan on Legends of Tomorrow's midseason premiere.

A self-proclaimed "exorcist, demonologist and master of the dark arts," John Constantine first appeared as a supporting character in Alan Moore's legendary Swamp Thing run. Going on to headline his own horror series, Hellblazer, John became a mainstay of DC Comics' mature readers imprint Vertigo. The NBC series based on the character was short-lived, but Matt Ryan proved popular enough in the role to be recast as John Constantine in the Justice League Dark animated film and to make a cameo in the Arrow episode "Haunted." It was this episode that confirmed Constantine's place in the Arrowverse, as he used his magical expertise to help resurrect Sara "White Canary" Lance.

Related: Legends of Tomorrow Midseason Return Synopsis: Constantine Needs Help

The augmented reality Easter egg was revealed in a photo posted on the Twitter for the Legends of Tomorrow writers. The photo depicts a torn scrap of paper with a phone number written on it - a phone number instantly recognizable to Constantine fans as the number from John Constantine's business card.

Fans who called the number in the days leading up to the original Constantine series airing were treated to a voice message from a surly John, advising those who were calling him to get a hold of Alec Holland (i.e. the scientist who became Swamp Thing) to "try the bloody swamp." Later, the message was changed, with John crudely insulting anyone who reached the number in error and instructing anyone who actually had called his number looking for his help not to leave a number and lock their doors.

At present time, calling the above phone number will give callers the second message. With a new Constantine animated series due to come out sometime in 2018, however, there's a chance that the phone line may have new messages for John's fans to laugh at in the months to come. Even if there isn't, it's nice to see that The CW revived the classic phone number for the sake of a good gag and that the writers of Legends of Tomorrow aren't letting people forget about where John Constantine came from.

More: Constantine Joins Legends of Tomorrow in Midseason Premiere Photos

Legends of Tomorrow returns on Monday, February 12, at 8 PM EST on The CW. Constantine: The Animated Series is due for release on The CW Seed sometime in 2018.

Source: Legends of Tomorrow Writers Room