Stranger Things and Marvel star David Harbour has seemingly confirmed a huge reveal from Avengers: Doomsday.

Speaking with Variety, Harbour was asked to recite a line of dialogue from the upcoming Marvel blockbuster out of context. Rather than decline the offer, Harbour instead offered up a choice quote that fans have taken as confirmation of a major story beat.

Warning! Potential Avengers: Doomsday spoiler follows:

"You... are Tony Stark," Harbour said, using the Russian accent of his Red Guardian character.

The dialogue appears to confirm that the inevitable reveal of Doctor Doom sharing a face with the MCU's Tony Stark will take place at some point within Avengers: Doomsday, and that Red Guardian at least will be present when it occurs. It's also, of course, a neat riff on Downey Jr.'s iconic "I am Iron Man" line — his final words as Tony Stark in the MCU to date.

While it seemed inevitable that the MCU's heroes would eventually discover Robert Downey Jr. under Doom's helmet, fans have been debating when exactly this reveal would take place, with some suggesting it would be saved for Avengers: Secret Wars.

Either way, it is surprising to see Harbour reveal this dialogue now, as it will no doubt be a key moment within the film. It's easy to imagine the shock that some former allies of Tony Stark will express on discovering the news, particularly among veteran Avengers such as Chris Evans' Steve Rogers and Chris Hemsworth's Thor.

Why does Doctor Doom look like Tony Stark? Apart from the obvious answer that Marvel wanted Downey Jr. back, the MCU looks set to confirm that Doom himself originates from the Fantastic Four's reality — a different branch of the multiverse from the main 616 timeline. So, two versions of the same person are possible.

Doom first appeared at the end of The Fantastic Four: First Steps, of course, though Doomsday's most recent trailer also seemed to confirm that he had been known to Sue Storm for some time as Victor. Exactly how he became the all-powerful Doctor Doom remains to be seen however, though fans certainly have some theories.

The past year has seen Harbour weather high-profile stories detailing elements of his private life with singer Lily Allen, and a seemingly-repaired working relationship with Stranger Things co-star Millie Bobbie Brown, who he will soon star again alongside in a fresh Netflix project. Alongside Doomsday, Harbour has also reportedly joined the cast of John Rambo.

Image credit: Chris Delmas / AFP via Getty Images.

Tom Phillips is IGN's News Editor. You can reach Tom at tom_phillips@ign.com or find him on Bluesky @tomphillipseg.bsky.social