Finally, at long last, the Avengers are assembling again!

This much-anticipated reunion of Earth’s Mightiest heroes can’t come soon enough. It’s been six difficult years for movie theater owners since their last heroic team-up in 2019’s “Avengers: Endgame.”

To the thrill of exhibitors from Seattle to Key West, Disney unveiled the first full-length trailer for “Avengers: Doomsday” at CinemaCon as part of the studio’s presentation to theater owners. Until now, Marvel has only offered four brief teasers focusing on Steve Rogers (formerly known as Captain America), Thor, the X-Men and the Fantastic Four, all answering the ultimate call to battle.

The trailer starts with a look at Downey Jr.’s green-hooded, metal-faced Doctor Doom as he prepares to invade the multiverse. There’s a shot of Professor Xavier (Patrick Stewart) looking out his X-Mansion’s window as a bright flash of light is outside, signaling trouble. It’s a flood of crossovers from there: Gambit (Channing Tatum) and Shang-Chi (Simu Liu) battle; Mystique (Rebecca Romijn) transforms into Yelena Belova, resulting in a Florence Pugh vs. Florence Pugh fight; and Thor (Chris Hemsworth) and Doom face off, but Doom catches Thor’s magical hammer Mjolnir with his bare hands.

The biggest moment comes when Chris Evans’ Steve Rogers makes his triumphant return and reunites with Thor. The Asgardian is shocked at his Avengers teammate’s arrival — given that Cap had gone back in time to grow old with his sweetheart Peggy Carter in “Endgame” (and passed down the mantle to Sam Wilson). It’s still unclear how Cap is back, but he’s clearly still worthy enough to pick up Thor’s hammer, just like he did during the Thanos battle in “Endgame.”

Similar to how “Infinity War” and “Endgame” brought together the Guardians of the Galaxy, the Wakandans and the Avengers, “Doomsday” intermixes Earth’s Mightiest Heroes with the X-Men, the Fantastic Four and the Thunderbolts. After the Fantastic Four’s ship crossed into the MCU in the post-credits scene of “Thunderbolts,” we finally see Mr. Fantastic, Invisible Woman, Human Torch and Thing meeting the so-called New Avengers (consisting of Bucky Barnes, Yelena Belova, Sentry, Ghost, Red Guardian and U.S. Agent). There’s also a tense showdown between Black Panther’s Wakandan forces and Namor’s underwater Talokans after the two armies clashed in “Wakanda Forever.”

All the heroes (and several former villains) must put aside their differences and join forces to take down Doctor Doom. Downey Jr., who narrates some of the trailer in a vaguely Eastern European accent, took the stage with Evans to play the trailer twice for the packed auditorium.

Joe and Anthony Russo are directing “Doomsday” and 2027’s “Avengers: Secret Wars,” which will conclude the Multiverse Saga of the MCU. The filmmakers have alluded to the idea that the back-to-back tentpoles will be connected, à la the two-part story of 2018’s “Avengers: Infinity War” and “Endgame.”

Plot details for “Doomsday” have been kept under wraps, but it promises to be the superhero extravaganza of this or really any year, “Doomsday” features a kitchen sink of Avengers and X-Men, including Paul Rudd as Ant-Man, Anthony Mackie as Sam Wilson, Pedro Pascal as Mister Fantastic, Ian McKellen as Magneto, Letitia Wright as Shuri, Tom Hiddleston as Loki and many, many more heroes.

Although Marvel’s recent track record has been rocky, the comic book empire’s biggest post-pandemic hits were major “Avengers”-esque team-ups, including 2021’s “Spider-Man: No Way Home” ($1.9 billion) and 2024’s “Deadpool & Wolverine” ($1.33 billion). Exhibitors are giddy about “Doomsday” because the last time that Disney’s Marvel Cinematic Universe assembled the entire gang was 2019’s “Avengers: Endgame,” which powered the biggest opening weekend of all time with $357 million domestically and $1.2 billion globally. “Endgame” triumphantly left theaters as the highest-grossing movie of the year and the second-largest in history with a staggering $2.8 billion worldwide.

“Avengers: Doomsday” is scheduled to open on the same day as “Dune: Part III,” which could result in one of the biggest collective weekends in box office history. “Avengers: Secret Wars” is expected to land a year later on Dec. 17, 2027.