In fact, one of the actors just Tom Holland-ed it during one of the interviews.
Back in 2016, the actors were asked to react to some of the fan theories about the show and the way the story could develop. It was the time of season 1, so a lot of questions that are answered now were a mystery back then.
But now that we know who was behind the supernatural evils haunting Hawkins, the interview just seems to be a huge spoiler – especially when we listen to a fan theory that Gaten Matarazzo (Dustin Henderson in the show) had enjoyed back at the time.
"There's this one in this video and he was saying how other test subjects, besides Eleven, One through Ten, most of them were dead, but the others were banished to the Upside Down. Like, they couldn't get out," Gaten recalled. "Because they were in the Upside Down for so long, and you can see that it had an effect on Will, it had an effect on them because they were in it for so long that they transformed into what was the monster. So the monster was a recent test subject."
With season 4 basically confirming this fan theory, it's curious to know whether Matarazzo actually knew that things will turn out to be that way and just decided that a forest was the best place to hide the tree, or if he (as well as the fan theory author) simply guessed it right.
Now we know that it was indeed about a certain test subject, Henry Creel a.k.a. Number One a.k.a. Vecna, being banished into the Upside Down by Eleven and evolving into a tentacle-wielding monster who torments people with their guilt by weaponizing their guilt and trauma.
It's even funnier to watch Millie Bobby Brown's reaction to the fan theory that predicted it because she suggested that her character, Eleven, could be the monster. This is not exactly how things turned out, but Eleven did become a part of an event that created Vecna by being the one who banished Number One to the Upside Down.
So next time you stumble upon a curious 'Stranger Things' fan theory, keep in mind that it could actually predict how the show will turn out to be. With the fifth and final season of the Netflix hit already in the works, there are just so many fan theories that could just be it, you know?