After being teased in Doctor Strange and Avengers: Endgame, it appears the Marvel Cinematic Universe is about to introduce the Marvel Multiverse. The latest Spider-Man: Far From Home trailer dropped that bombshell when it revealed that Jake Gyllenhaal's Quentin Beck/Mysterio actually comes from an alternate Earth. Apparently, one of the Infinity Gauntlet's reality-altering snaps was enough to tear a hole across dimensions, and now Beck has stumbled onto an Earth that is not his own.

The movie's first clip features the initial meeting between Mysterio and Spider-Man. There, the dimension-hopping Beck informs the young Peter Parker that the planet Spider-Man is from is dubbed "Earth Dimension 616."

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Most fans have taken the clip as the first mention of the classic Earth-616 designation in the MCU -- but that's not exactly accurate. In fact, Earth being numbered 616 first came up in a previous film: 2013's Thor: The Dark World.

Mysterio in Spider-Man: Far From Home

For the most part, Marvel Comics tells the stories of one specific Earth, the place characters like the Avengers, Spider-Man and the Fantastic Four call home. However, this is just one of an infinite number of parallel realities, and so, the prime Earth has been given a designation: Earth-616.

The designation debuted in 1983, in a story by Alan Moore and Alan Davis, which showed Captain Britain meeting the Captain Britain Corps, which is comprised of other versions of the character from alternate dimensions. Captain Britain was classified as the one from Earth-616, while others came from differently numbered realities. Since then, Earth-616 has become the official designation for the prime Marvel Universe, and it is used in any story that involves the Multiverse, such as 2014's Spider-Verse or 2015's Secret Wars.

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With the Multiverse officially set to make its MCU debut in Far From Home, it only stands to reason that the homeworld of Peter Parker and the rest of Earth's Mightiest Heroes would be dubbed Earth-616 -- the first mention of which actually came six years ago, in Thor: The Dark World.

The Thor sequel featured a Dr. Erik Selvig who was much different from the version met in the previous Thor film. After falling under the effects of the Tesseract in The Avengers, Selvig was left a rambling mess. He was still a brilliant scientist, but his mind had been open to a universe's worth of knowledge, and he had trouble coping with all of it. As a result, Selvig found himself institutionalized for a spell.

Thor-The-Dark-World-Erik-Selvig

While in the care of a psychiatric facility, Selvig filled a chalkboard with notes about the MCU cosmos. On that board, there was one very notable entry: "616 universe."

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That's right -- years before Mysterio's arrival, Dr. Selvig already knew that his reality was numbered 616 in the vast multiverse. Since the Tesseract (which we now know was the Space Stone) revealed all sorts of information to him, it's probable that it showed him the space occupied by all realities -- all universes. And in this newfound knowledge was the information that the designation for his reality was the 616 universe.

The reference in The Dark World is subtle -- you have to pay attention to catch it -- but it's there, and potentially more significant than ever.

Opening July 2, director Jon Watts’ Spider-Man: Far From Home stars Tom Holland, Samuel L. Jackson, Zendaya, Cobie Smulders, Jon Favreau, JB Smoove, Jacob Batalon and Martin Starr, with Marisa Tomei and Jake Gyllenhaal. Avengers: Endgame is currently in theaters.