The first Avengers: Endgame release trailer has been online for less than a day, but the theories on how Marvel will connect the 2019 movie to Avengers: Doomsday are already coming in thick and fast. But one fan may have already cracked the code.

“Doctor Doom is the reason Doctor Strange saw only ONE universe where the Avengers won,” said Mavel Mania on Twitter, adding that they believe Doom is actually a Tony Stark variant. “One Tony variant could have survived the snap or found another way to defeat Thanos without sacrificing himself. Strange saw what Tony would eventually become and deliberately pushed him toward the sacrifice, preventing the future where Tony became Doom.”

If true, this would explain why Marvel chose to cast Downey, who played Tony Stark in the MCU for over a decade, as Doctor Doom. If Doctor Strange saw an alternate timeline where Stark would survive, but would be a villain, it is no surprise that he chose the timeline where the Avengers beat Thanos, even if that did mean letting Stark die.

The upcoming re-release, officially titled Avengers Endgame Encore, promises to bridge the gap between the 2019 film and Doomsday, including four extra minutes of footage. In an interview with Fandango, director Joe Russo said, “There’s a natural progression from Endgame into Doomsday… I think it’s required viewing for following the story in Doomsday.”

The fan theory also explains why Chris Evans’ Steve Rogers is back in the present timeline looking the same-ish age he did in Endgame. “He could be from that same universe, where the Endgame battle still happened, Tony survived, and Steve never truly retired.” Rogers’ return has left many Marvel fans puzzled, as the last time we saw Rogers, he went back in time to live out his life with Peggy Carter. Then when he was old and grey, he handed the Captain America mantle to Sam Wilson.

Avengers: Endgame Encore is out in cinemas on September 25. For more, check out our guides to Marvel Phase 6 and upcoming Marvel movies.