The Marvel Cinematic Universe has always hidden Easter eggs for fans to discover, from simple nods to the comic book source material to the building blocks of the superhero franchise. With Avengers: Endgame released last week on digital, fans are free to pore over the three-hour film in hopes of uncovering all of its secrets, such as the apparent shoutout to Spider-Gwen.

On Reddit, a fan shared his discovery of the MCU's latest reference to "616," which appears early in the blockbuster, when Scott Lang returns from the Quantum Realm after a benevolent mouse turns on the Quantum Tunnel. Lang is blasted out of the van and into a locked storage unit. In the unit, a handwritten sign reads "Lang," to identify the owner of the belongings. Underneath the name is the unit number, "616."

That number holds a special significance to comic book fans, as the designation for the prime reality of the Marvel universe. Most of the superheroes that appear in the comic books live in one universe, known as 616, which is part of the multiverse.

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This nod to the multiverse is far from the first in the MCU. In fact, in 2013's Thor: The Dark World, Erik Selvig wrote the number on a board filled with his cosmic ramblings. Because of the Tesseract, the physicist gained knowledge from the entire universe, and the implication was that he might have glimpsed the multiverse.

The number was also mentioned in Spider-Man: Far From Home, when Quentin Beck, aka Mysterio, said he was a traveler from another reality. He designated Peter Parker's world as "Earth-616." Of course, it turned out that Beck was lying about everything. However, as a scientist who had a vast network of brilliant minds to help him, it's possible that his lies were based on the truth.

Finally, Season 2 of Iron Fist also featured a "616" mention, when it was revealed as the code police used to describe a possible suspect with superpowers.

This Avengers: Endgame Easter egg is just the latest nod to the Marvel multiverse. With Doctor Strange in the Madness of the Multiverse coming soon, we are finally bound to witness a payoff to something that Marvel has been seeding for a long time.

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Directed by Joe and Anthony Russo, Avengers: Endgame stars Robert Downey Jr. as Iron Man, Chris Evans as Captain America, Mark Ruffalo as Bruce Banner, Chris Hemsworth as Thor, Scarlett Johansson as Black Widow, Jeremy Renner as Hawkeye, Brie Larson as Captain Marvel, Paul Rudd as Ant-Man, Don Cheadle as War Machine, Karen Gillan as Nebula, Danai Gurira as Okoye and Bradley Cooper as Rocket, with Gwyneth Paltrow Pepper Potts, Jon Favreau as Happy Hogan, Benedict Wong as Wong, Tessa Thompson as Valkyrie and Josh Brolin as Thanos. The film is now available on Digital HD and arrives Aug. 13 on Blu-ray and 4K UHD.