In the video above, from back in 2016—right after the first season of Stranger Things aired—Gaten Matarazzo described a fan theory from Reddit that kinda nailed the plot twist of Season 4.
"It was crazy, I was just reading a fan theory off of Reddit that was apparently spot-on. I'm just so happy that it didn't go viral until after [Season 4]," Gaten told Seventeen in a new interview. "It was surprisingly accurate. I'm glad it didn't gain too much traction before the show came out."