The following contains spoilers for Immortal X-Men #10, now on sale from Marvel Comics.

The X-Men's most dangerous internal threats have become a serious concern lately, with figures like Storm and groups like X-Force doing their best to handle ambitious threats like Vulcan, Abigail Brand, and Beast. But one of Krakoa's most dangerous figures is finally making their ultimate play, and it could seriously up-end the future of the mutant nation.

Immortal X-Men #10 (by Kieron Gillen, Lucas Werneck, David Curiel, and VC's Clayton Cowles) confirms that Mister Sinister has taken control of Charles Xavier. This is a massive danger to the entire world given Xavier's power-set -- and could seriously bring some unwanted attention to the X-Men.

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Professor X is Under the Control of Mister Sinister

X-Men Xavier Immortal Sinister Header

Mister Sinister has been a lingering threat throughout the Krakoa Era. His important role in providing invaluable DNA samples making resurrection a real possibility for the growing mutant nation has made him a devil the heroes have to deal with, and as a result, he was given a place within the Quiet Council. But his attempts to gain more power (such as creating an Omega-Level Chimera body for himself in Hellions) have been countered by other prominent mutants. As the tide increasingly turns against him and suspicious rises as a result of Dr. Stasis and Orbis Stellaris being exposed as fellow Sinister copies, Sinister finally decided to go on the offensive -- slaughtering a quarter of the Quiet Council in a surprise attack that seemed to successfully derail resurrection by killing Hope Summers.

However, things seem to quickly turn against Sinister, as Synch is able to successfully replace Hope within the Five's very specific power circuit. As a result, the full Quiet Council accompanies the X-Men on their hunt for Sinister, who is promptly overwhelmed and captured. It isn't long before Sinister is condemned to the Pit, and the Quiet Council announce their intention to move forward without monsters like Sinister trying to influence them. But as Xavier returns to his private quarters, he removes Cerebro and reveals a distinctive Sinister diamond on his head -- suggesting Xavier is either under the full control of the villain or has had his personality supplanted by Sinister, giving him access to all of Xavier's wide-ranging psychic potential.

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A Sinister-Controlled Professor X is Terrifying

Immortal X-Men 10 panel showing Xavier with a Sinister gem on his forehead

It's a major development for the X-Men and the Marvel Universe at large, as Xavier remains one of Marvel's most powerful telepaths. While he may not quite reach Omega-Level classification, Xavier's internal monologue throughout the issue reflects on his ability to wipe out entire populations if he so wished with just a thought -- and that someone like Mister Sinister or Magneto having that kind of power could have led to the full eradication of humanity or mutants as an entire species. Xavier being taken under control by Sinister isn't exactly a new plan, as the villain attempted something similar years ago as a part of the X-Men Legacy series. But whereas that scheme was seemingly halted, it appears Sinister was able at some point to successfully infect Xavier with his influence.

It's likely that Xavier's impressive psychic capabilities will play a major role in the setup for Sins of Sinister, as his extensive psychic abilities could be an easy means of setting up a completely different Marvel Universe where Mister Sinister effectively won. A villainous Xavier is a true danger, as entities like Onslaught have taken extreme measures to counter and other worlds have highlighted he could become a mass murderer on a truly terrifying scale. Xavier even briefly falling under his control could result in some serious damage to the world at large, and may give the rest of humanity a real good reason to fear mutants even if they successfully break Mister Sinister's control on the world -- potentially giving Orchis the perfect opening to set about the Fall of X to bring about the end of the X-Men's most important period in years.