Marvel fans need to prepare for "a very surprising ending" to Avengers: Doomsday, directors Joe and Anthony Russo have teased.

Speaking to Fandango, Anthony Russo described the upcoming Marvel blockbuster as a "focused propulsive narrative," while still weighing in as one of the studio's longest films to date.

As you might expect from a movie with such a large cast, Avengers: Doomsday will clock in around the "two-and-half hour" mark, though even the Russos are unlikely to know the exact runtime just yet as reshoots were believed to be taking place only this month to add even more material.

Only three Marvel movies have ever stretched longer than two-and-a-half hours (150 minutes), with the appropriately named Eternals at an everlasting 157 minutes, Black Panther: Wakanda takes Forever at 161 minutes, and Avengers never Endgame at a whopping three hours and one minute (or 181 minutes total).

Still, Anthony Russo suggested Avengers: Doomsday audiences wouldn't be bored.

"It's a two-and-a-half hour movie or so, and you're sitting through it, and it's a focused propulsive narrative that has an organizing principle at its center, and everything has to orbit around that," he said. "That's part of the creative challenge for Joe and I — just figuring out what that orbit is and how it all smashes together."

As for how it all concludes — and leads into next year's climactic Avengers: Secret Wars — the Russo brothers had this to say:

"I think people are going to be surprised," Joe Russo teased. "It's a very surprising ending. It's a very surprising movie and that's all we'll say about it."

What could this mean? Well, with Doomsday being just part one of the story, it seems clear the movie will not end Doctor Doom's story just yet, and therefore it seems extremely unlikely the film will wrap everything up with a happy ending.

Even without knowledge of the Secret Wars comics or informed speculation based on filming leaks and reports, it seems fair to compare Doomsday to Infinity War, the first film in the Russo brothers' previous Avengers two-parter. That movie ended with the Avengers losing to Thanos, with multiple main character deaths throughout the film that were not reversed, then a climactic event that acted as a shocking cliffhanger. Will the Avengers lose again to Doctor Doom? I would not describe this as too surprising, but it would certainly serve as an interesting jumping off point for Secret Wars, should it follow the Marvel comics' general story.

The Russos have been doing the rounds promoting Avengers: Endgame Encore, which features four brand new scenes they have confirmed won't appear in Doomsday itself. One of these scenes sees Doom "collect" the Hulk, potentially suggesting he will sit out Doomsday and return in Secret Wars. Avengers: Doomsday launches in theaters on December 18.

Tom Phillips is IGN's News Editor. You can reach Tom at [email protected] or find him on Bluesky @tomphillipseg.bsky.social