With the stakes for the Marvel Cinematic Universe higher than they've ever been before, not every fan-favorite superhero is guaranteed to walk away from Avengers: Endgame. A new fan theory suggests one hero in particular will lay his life on the line and make the ultimate sacrifice to ensure an estranged friend and comrade-in-arms survives in his place.

Posted on Reddit by the user Farores_Winds, the new theory posits that Endgame's climax culminates in Steve Rogers' sacrificing his life to save a pregnant Pepper Potts from Thanos. The heroic death would serve as a continuation of the recurring theme of family between Rogers and Tony Stark, which has been steadily building since their introductions into the MCU. It would also serve as a bittersweet reconciliation of sorts between the two men after their falling out in Captain America: Civil War.

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The full theory has Pepper take on the armored alter ego of Rescue to join in the fight and save her fiancé, Tony, while carrying their unborn child. As Thanos prepares to kill Pepper before Tony's eyes, Captain America intervenes and dies, saving Pepper's life instead. Enraged over the death of his one-time friend and ally, Tony personally kills the Mad Titan and retires from his career as a superhero to quietly raise his family with Pepper.

While the play-by-play prediction is highly unlikely to follow exactly as described in the fan theory, it does highlight several recurring themes for Iron Man and Captain America throughout their respective histories in the MCU. More pragmatically, it also provides both veteran actors with a noble way out as their contracts with Marvel Studios come to an end with the completion of Avengers: Endgame, while also honoring the characters they've developed for years.

Tony Stark's character arc ever since the inaugural MCU film, 2008's Iron Man, has been about his personal redemption. The former arms dealer became a superhero to defend the world from the very weapons he invented and sold, later starting a long-term relationship with Stark Industries CEO Pepper Potts.

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Coping with the tremendous guilt of inadvertently creating Ultron, Tony and Steve came to blows, with Tony especially incensed after learning a brainwashed Bucky Barnes was responsible for the deaths of his parents decades ago. Following Tony proposing to Pepper in Spider-Man: Homecoming, the Iron Avenger has a premonition in Avengers: Infinity War of Pepper being pregnant with their child, which is strongly rumored to come true in Endgame.

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For Steve Rogers, any hopes of the Star-Spangled Avenger having a happy domestic life died in the ice at the end of World War II. Cryogenically frozen for nearly 70 years, Captain America pointedly avoided personal relationships following his reintegration into modern society, even becoming visibly uncomfortable talking about his romantic prospects throughout Captain America: The Winter Soldier. In a written letter to Tony in the final moments of Civil War, Steve confesses that the Avengers have become more of a family to Tony than himself, and that his armored ally needs them as much as they do him.

Chris Evans in Avengers: Infinity War

The rupture of the Avengers in Civil War is felt all throughout Infinity War. At no point do Tony Stark or Steve Rogers interact directly in the entire film, with Bruce Banner ultimately being the one to notify Steve of Thanos' impending arrival. Endgame will mark the reunion of the estranged allies and offer the two men the chance for one final reconciliation before their inevitable rematch with the Mad Titan. It also offers Steve Rogers the chance to sacrifice his life to guarantee Tony and Pepper the one thing that he could never truly enjoy himself: domesticity.

In perhaps the most prophetic MCU film, Avengers: Age of Ultron, Tony Stark first learns of Thanos' existence, setting him on an obsessive course that causes the creation of Ultron, the dissolution of the Avengers and a temporary break-up with Pepper. Endgame offers the Armored Avenger the chance to redeem himself of that obsession, though it will place himself and those he cares for directly in harm's way, as seen with the death of his surrogate son, Peter Parker, in Infinity War.

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While Steve Rogers has insisted that the Avengers don't trade lives, the sacrifice play is one he first advocated for during an argument with Tony in 2012's The Avengers. Steve is already on a desperate mission to save Bucky at potentially the cost of his own life in Endgame. Perhaps, in a final act of reconciliation, Steve will also sacrifice himself to give Tony the domestic life he urged him to pursue in the final moments of Age of Ultron. It would allow Chris Evans to have the noble exit he deserves and give Robert Downey Jr. a dignified way to exit the MCU, but still exist in the periphery if he so chooses.

Captain America: Civil War was about division; Avengers: Infinity War about facing certain defeat. Avengers: Endgame will likely revolve around the theme of heroic sacrifice, and the noblest Avenger of them all is the most likely to pay the price.

Directed by Joe and Anthony Russo, Avengers: Endgame stars Robert Downey Jr., Josh Brolin, Mark Ruffalo, Tom Hiddleston, Chris Evans, Chris Hemsworth, Jeremy Renner, Chris Pratt, Elizabeth Olsen, Chadwick Boseman, Sebastian Stan, Benedict Cumberbatch, Paul Bettany, Samuel L. Jackson, Cobie Smulders, Benedict Wong, Zoe Saldana, Karen Gillan, Vin Diesel, Dave Bautista, Pom Klementieff, Scarlett Johansson, Tom Holland and Anthony Mackie. The film is set to be released on April 26.