The MCU has been chugging along since 2008, and it has slowly become one of the biggest movie franchises of all time. This shared cinematic universe of superhero films began by introducing Iron Man to the audience, and went on to establish The Avengers as a powerful superhero team. It has even explored the far reaches of outer space in movies like Guardians of the Galaxy and Captain Marvel. Yet one question remains on fans' minds. When will the X-Men debut in the MCU?