The third teaser for Marvel's 'Avengers: Doomsday' officially confirms the return of iconic X-Men characters Professor X, Magneto, and Cyclops to the Marvel Cinematic Universe. The footage features Patrick Stewart, Ian McKellen, and James Marsden reprising their roles, with a somber tone and dialogue hinting at existential stakes. The teaser also showcases Cyclops unleashing a powerful optic blast and suggests a massive crossover event involving Avengers and Fantastic Four heroes, potentially against Doctor Doom.