Mystery Solved: 'Captain America 3' to Challenge Batman-Superman Head On (Exclusive)

Until now, the identity of the Marvel film set to open on May 6, 2016, has been kept secret; Marvel Studios and Disney claimed the date first before Warner Bros. slotted the next "Superman" installment for the same weekend.

The mystery has been solved -- the untitled Marvel Studios tentpole that Warner Bros.' Batman and Superman movie will go up against on May 6, 2016, is Captain America 3, sources tell The Hollywood Reporter.

That's the plan, anyway, creating the biggest superhero box office showdown in history. (Marvel Studios and parent company Disney staked out the date first.) Shooting schedules and postproduction could always impact the current blueprint, however. Also, Marvel and Disney have a second untitled movie scheduled to open that summer on July 8, so there is wiggle room.

Marvel films have all but owned the first weekend of summer for the past decade to enormous success, so all of Hollywood was surprised when Warner Bros. announced in January that it would open Batman-Superman on May 6, 2016 as well.

Batman-Superman stars Ben Affleck as Batman and Henry Cavill once again as Superman. It was originally supposed to hit theaters in summer 2015, but its release was pushed back nearly a year. There's no doubt that Warner Bros. is hoping to replicate the blockbuster returns Marvel has enjoyed with its multihero Avengers universe.

EARLIER: Batman-Superman Movie Bumped to 2016, Setting Up Marvel Showdown 

This week, when promoting the upcoming sequel Captain America: The Winter Soldier, Marvel Studios president Kevin Feige threw down the gauntlet, saying he had no plans to move off the May 6 date. He still wouldn't reveal the identity of the film; however, insiders confirm it will indeed be Captain America 3. The world premiere of Winter Soldier is Thursday in Hollywood.

Warner Bros. may have been waiting to see what the Marvel title was before considering a date change for Batman-Superman, if the studio blinks. There are still weekends available that summer, including the first two after Captain America 3 and Batman-Superman are set to open. Zack Snyder begins shooting Batman-Superman in the coming weeks.

Veteran box office observers doubt that the two films will ultimately open opposite each other.

Marvel and Disney are incredibly high on Captain America 2, which opens in north America on April 4 and is garnering huge interest, according to prerelease tracking. They believe Winter Soldier, with Chris Evans returning in the title role, will benefit from the same halo effect from The Avengers that Iron Man 3 and sequel Thor: The Dark World enjoyed, as well as firmly establishing Captain America as a standalone franchise.

Brothers Anthony and Joe Russo directed Winter Soldier and are in talks to return for Captain America 3.

The first, Captain America: The First Avenger, took in $371 million worldwide, compared to $668 million for Man of Steel. However, Winter Soldier has a shot at matching the $641 million grossed worldwide by fellow Marvel sequel Thor: The Dark World late last year.

Borys Kit contributed to this report.