While Alan Taylor's Thor: The Dark World might not be the best-loved movie in the Marvel Cinematic Universe, it turns out the Thor sequel has an X-Men reference hiding in plain sight.
Despite Thor: The Dark World's divisive reception, what Taylor delivered was an important post-Avengers outing and notably introduced the Reality Stone to the MCU. However, the fact Taylor made a nod to the X-Men just added another layer to the 2013 movie.
According to Screen Rant, fans should rewatch the scene where Stellan Skarsgård's Erik Selvig tries to explain the Convergence to bewildered patients in the asylum he's locked in. As well as featuring Stan Lee's signature cameo, Selvig's chalkboard ramblings also mention a phenomenon called the Fault. Those up on their comic book history will know the Fault was the result of a brutal Shi'ar and Kree war that revolved around the villainous Vulcan.
Vulcan was first introduced in 2006's X-Men: Deadly Genesis #1 and emerged as a powerful Omega-level mutant. During the war, which Vulcan started, the Kree detonated a deadly T-bomb that created the Fault, causing a tear in the fabric of time and space that lead into a void known as the Cancerverse. The Canververse is a major plot point in Jonathan Hickman's comic book reboot and is the breeding ground for the parasitic race known as the Brood.
With the merger between Fox and Disney, it is only a matter of time before the X-Men join the Marvel Cinematic Universe. Kevin Feige confirmed at San Diego Comic-Con International 2019 that the mutants would make their debut in the MCU, but did not give any further details.