'X-Men: Apocalypse' sets the stage for its most powerful mutant to be unleashed in future films

"X-Men: Apocalypse" pits a new class of young heroes against Apocalypse, the original mutant. Apocalypse can destroy entire cities with little more than a hand gesture and wants to destroy the planet and remake it with a new mutant world order where he rules as a god.

At his side are Four Horsemen. Powerful in the own right, Apocalypse uses his abilities to strengthen them even further.

Given the high caliber of mutants onscreen in "Apocalypse," it comes as a huge shock when, in the last act, one character is revealed to have powers rivaling that of the ancient God.

Warning: There are spoilers ahead if you have not seen "X-Men: Apocalypse."

Jean Grey.

She spends much of the film trying to repress her powers and is a quiet, but confident, tagalong for much of the film. So when she steps onto the center stage and takes down the most powerful mutan it's a shock.

As Xavier loses the battle in his own mind against Apocalypse, he cries out to Jean Grey, telling her: "Let go." Jean focuses her full strength onto Apocalypse and, emanating brilliant rays of light, lets out a piercing scream that literally melts the face off Apocalypse. His skin, muscle, and finally bones, peel away and turn to ash. While he still has lips left to speak, he whispers aloud "All is revealed." We know Jean struggled to control her powers, but how could she should kill an ancient would-be god in only a few moments? And what does it mean for her future appearances? Enter: the Dark Phoenix.

Jean tapped into the powers of the Phoenix Force to defeat Apocalypse. The Phoenix Force is sentient, cosmic energy of immeasurable power. In the comics, Jean comes into contact with the Phoenix Force while traveling through space, but in the films, she's born with the connection. As the name implies, the Phoenix has full power over life and death, and can destroy and absorb the solar energy of stars and planets.

Jean and the Phoenix Force are inseparable, yet as Jean taps into its strength, she loses herself to its appetite for destruction. In a comic event known as "The Dark Phoenix Saga," the Phoenix Force took full control of Jean and began devouring stars, killing thousands of people across the galaxy. This set off a series of intergalactic conflicts across multiple issues and established the Dark Phoenix as one of the most powerful enemies in Marvel history.

Given its status as such a revered character arc, fans are very cautious about how studios will approach showing Dark Phoenix onscreen. With early speculation that an "Apocalypse" sequel may cover the Dark Phoenix arc, fans are hesitant that it may have been introduced too soon. The original "X-Men" trilogy teased Dark Phoenix for two films before her appearance in the "X-Men: The Last Stand," but fans and critics agree that version of the character was muddled and disappointing. How slowly or quickly Dark Phoenix is introduced isn't the issue, it's the execution. And if Jean's powers are already being teased, it's better to address the storyline while it's fresh in audience's minds.

It remains to be seen how they'll handle this storyline on screen, but Sophie Turner teased to EW that Phoenix is key to the future of the franchise: "The seeds of Phoenix definitely are planted in there. There are definitely, like, bits and pieces, but I think in future movies to come we'll definitely see a bit more of that."