Spoilers ahead for Batman V Superman: Dawn of Justice, in theaters now.

During Batman V Superman: Dawn of Justice's opening weekend, hardcore comic book fans were pretty sure they knew what it was Silas Stone used to transform his dismembered and dying son into the being we will all come to know as Cyborg in next year's Justice League Part One.

Casual fans, of course, were likely baffled, as the mysterious, moving box wasn't named or explained, other than to say it was an alien artifact.

Well, Batman V Superman and Justice League director Zack Snyder has now confirmed that the item fans saw in that scene was indeed a Mother Box.

“That’s the first glimpse of the Mother Box there,” Snyder told EW of Cyborg's origin, which was glimpsed briefly in Batman V Superman. “It was an agonizing birth.”

It seems likely that we'll soon start to learn much more about how Jack Kirby's Fourth World plays into the film; the Knightmare sequence featured Parademons, Cyborg's origin featured a Mother Box, and a deleted scene released earlier today featured what looks like either Steppenwolf or Yuga Khan, both emissaries of Darkseid, ruler of Apokolips.

Mother Boxes attach themselves to a host and help them in whatever way they need. Fourth World characters like Mister Miracle are the ones most commonly depicted as using them, but following DC Comics's 2011 "New 52" reboot, Cyborg's backstory was adjusted to include powers granted by a Mother Box.

Justice League Part One is expected to start filming in April for a release on November 17, 2017.

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Batman v. Superman: Dawn of Justice is now playing in theaters.