There's a brief shot in the just-released trailer for Guardians of the Galaxy Vol. 3 of the film's villain, the High Evolutionary, watching over a child with stark white skin and hair as she runs on a treadmill, presumably part of one of his experiments in creating highly evolved forms of life (as his name implies).
Now, we're gonna preface this next bit by saying it's… maybe a bit of a wild guess… considering the unnamed child is only seen in a single shot of the trailer.
But that kid looks one hell of a lot like Black Swan, a character taken from writer Jonathan Hickman's long Avengers run which led up to the 2015 event Secret Wars - which provides some inspiration for the upcoming MCU film of the same name.
Black Swan is actually named Yabbat Ummon Turu, and she's just one of a group of women warriors named the Black Swans from across Marvel's Multiverse who serve a so-called "Great Destroyer" named Rabun Alal.
Yabbat Ummon Turu discovers the truth about Rabun Alal, betraying him and using her station as a Black Swan to begin destroying realities as part of the Multiversal Incursions that collapsed Marvel's Multiverse in the lead up to Secret Wars, eventually coming into contact with the Avengers of the core Marvel reality as they work to save their own world.
So… What's the secret of Rabun Alal, the "Great Destroyer," that leads Black Swan to betray her master?
Well uh… He's actually Doctor Doom. Like, the core Marvel reality Doctor Doom, who has built a cult of Multiversal Black Swans as part of his own plan to save reality from the collapse of the Multiverse - the plot that leads directly to the start of Secret Wars.
So could that kid be a being from the Multiverse, even a Black Swan?
As we said, it's a wild guess based on her visual appearance (and the current Marvel Multiverse Saga that's unfolding in the MCU). But with Secret Wars on the horizon, and the concept of Incursions already in play (see the Multiverse of Madness post-credits scene), anything is possible.
Secret Wars is one of the best Marvel Comics events of all time.