'Avengers: Endgame' theory solves the biggest mystery in 'Black Widow'

Black Widow wraps up its twisty plot pretty well, with one major exception. Could this far-out Avengers: Endgame theory hold the answer to the movie’s lingering mystery?

Warning! Light spoilers ahead for the plot of Black Widow, and major spoilers for Endgame.

The mystery — About halfway through Black Widow, Natasha (Scarlet Johansson) and Yelena (Florence Pugh) team up to bust their adoptive Russian superhero father out of a Soviet-era prison. But Alexei (aka, Red Guardian, played by David Harbour) actually seems pretty happy. He’s spending his time winning arm wrestling matches, getting tattoos, and telling tall tales about how he once fought Captain America.

That’s right, Alexei claims to have fought Steve Rogers himself, which doesn’t exactly make sense. As another unfortunate prisoner points out, Cap went into the ice before Red Guardian got his powers, and by the time Rogers returned in 2011, Alexei was already locked up.

So is Alexei lying? Harbour and Black Widow director Cate Shortland wouldn’t give us a straight answer, but the truth may lie in one popular theory about Avengers: Endgame.

The theory — This one is pretty simple. What if every Stan Lee cameo in the Marvel Cinematic Universe was actually a post-Endgame Steve Rogers checking in on his friends? We’ve seen different versions of the theory pop up over the years, but the basic gist is that after Steve went back in time to live with Peggy Carter, he couldn’t resist going on a few secret missions of the years.

An extra wrinkle to this theory is that Stan Lee was actually supposed to play old Steve Rogers in Avengers: Endgame, which would have been pretty wild. However, that doesn’t totally make sense since he was still alive during filming and even has a cameo elsewhere in the movie. Still, this theory explains why Lee keeps popping up in the MCU. It’s also a helpful back-up now that earlier theories about Lee’s character actually being Uatu the Watcher have been disproven by the upcoming Disney+ series What If...?

And of course, if Steve Rogers really was popping up throughout MCU history, he easily could have run afoul of Red Guardian. Stan Lee had a cameo in Captain Marvel, which places his character in Marvel’s version of the ‘90s. So it’s not out of the question that he was out and about during the Cold War too.

To be fair, this is all a huge stretch. Marvel will probably never explain Stan Lee’s cameos because there’s no reason to explain them in the first place. Revealing that he was actually a time-travelling Steve Rogers or some sort of cosmic being would ruin the purity of those moments. But that gap in knowledge means fans will also be able to speculate and theorize for years to come.

The fact that this particular theory also solves a Black Widow mystery is just a bonus.

Black Widow is streaming now on Disney+.