David Harbour appears to have inadvertently confirmed a major plot point in the upcoming Marvel film Avengers: Doomsday. During an interview with Variety, when asked to recite an out-of-context line from the film, the Stranger Things actor delivered dialogue that fans believe reveals the film will explicitly confirm Doctor Doom shares a face with the MCU's Tony Stark, and that this reveal happens within Doomsday itself rather than being saved for the sequel Secret Wars.

Speaking in the Russian accent of his character Red Guardian, Harbour said "You… are Tony Stark," echoing Robert Downey Jr's famous "I am Iron Man" line. The MCU appears set to explain the resemblance by establishing that Doom originates from an alternate timeline linked to the Fantastic Four, whose reality was introduced in The Fantastic Four: First Steps, where the character first appeared as "Victor." Avengers: Doomsday is due for release on 18 December 2026.