Superman's wildest theory yet suggests the mystery trailer character is actually a secret Supergirl cameo

I've heard plenty of wild Superman theories already this year, but none quite like this explanation for how Supergirl is turning up in the DC movie.

While the Superman trailers have largely kept plot details under wraps, two mysteries are threads that fans keep on pulling at: who is the armor-plated Hammer of Boravia that's fighting Superman, and where is Supergirl?

In one fell swoop, one theorist has bundled the two together – and believes the Hammer of Boravia is Supergirl.

"What if Lex Luthor found her first?" @JuanSC wrote on Twitter. "Supergirl crash-lands on Earth, confused, disoriented… and Lex locks her inside the Boravia armor. Weaponized. Controlled. Dangerous."

He continued, "In the trailer, the Hammer uses Superman-level powers. That leaves us with 2 real options: – a robot built to copy Kryptonian powers – or Supergirl, trapped in the suit."

Those Superman-esque laser beams emanating from the Hammer of Boravia's eyes does suggest someone of Krypton origin is behind the helmet. Lex Luthor falsifying a response from the fictional country of Boravia in response to Superman in the hopes of leaving the Man of Steel as public enemy number #1 also rings true.

You may not be entirely convinced, but it's a narrative swerve as good as any we've seen so far – unless director James Gunn opts to put someone like Ultraman – the evil, alternate universe take on Superman – in the role.

Here's what we do know: Earlier this year, The Hollywood Reporter confirmed that Milly Alcock would be making her Supergirl debut in this year's Superman film before appearing in her own feature – Woman of Tomorrow – in 2026.

For now, Supergirl is one mystery that remains up in the air. But expect her to fly into Superman's orbit very soon.

Discover more about DC's new era with our guides to DCU Chapter One and new DC movies.