​Millie Bobby Brown's Eleven has always been the best character in Stranger Things—so much so that even when the story focuses on one of the series' other characters, audiences still can't help but wonder what's going on with Eleven. It didn't take long for the Duffer Brothers, the show's creators, to realize this—which meant they had to change their plans for her story arc.

In Stranger Things: World Turned Upside Down, a new companion book, the Duffer Brothers explain in the foreword that both ​Eleven and Steve Harrington, another beloved character, were originally going to be killed off in the first season.

“Eleven was going to sacrifice herself to save the day,” Ross Duffer reveals in the book, according to Esquire. “That was always the end game.

“But once we realized that the show was potentially going to go on longer than one season, we needed to leave it more up in the air, because deep down we knew the show just wouldn’t really work without Eleven," Duffer continues. "And at that point, we knew how special Millie was. If there was going to be more Stranger Things, Eleven had to come back.”

As for Steve, the book explains how his character was just supposed to be a bad guy who died in Season 1, but actor ​Joe Keery's popularity in the show made the creators change their minds.

The Duffer Brothers also reveal other major details about the series, such as that the original script for the pilot being called "Montauk," and the Upside-Down first being referred to as the Nether.

We've heard plenty of rumors regarding the third season of Stranger Things, but we won't know much for sure until it returns to Netflix next summer.