Millie Bobby Brown's breakout character from Netflix's hugely successful sci-fi show, Stranger Things, wasn't meant to live past the first season.

In fact, there wasn't even meant to be a second season in the first place - let alone a third and potentially fourth instalment.

Stranger Things co-founder Ross Duffer let slip that Eleven was originally meant to sacrifice herself in order to save her friends.

"Maybe I shouldn't say this because I like to pretend that it was all planned out, but [Stranger Things] was originally pitched as a limited series," he told students at California's Chapman University during a Q&A session. "So it was like, Eleven was gunna sacrifice herself and save the world and that was gunna be it, because there was a moment where limited series were a big deal."

Luckily for Millie Bobby Brown fans, that didn't happen. Instead, season one ends with Eleven vanquishing the demogorgon but - in doing so - trapping herself in the parallel universe known as the Upside Down.

"This is where the business side comes in," Duffer explained. "When we started pitching it, it was like 'we don't make money off of limited series'. And I remember when we went into Netflix and we pitched this, they were like, well we like this but how could it keep going?

"You're just sort of riffing in the moment and we were like, well Will's back from this other dimension and he's not doing very well. And they were like, great."

The revelations around Stranger Things originally being a limited series come as the show's writers have had to address more plot holes (although, admittedly, not to the same extent as everyone seemingly forgetting about Barb after she was killed in season one).

In one episode in season two, Dustin evicts his pet turtle from his tank to make room for his new slimy and seemingly friendly new friend, Dart. Dart later morphs into a cat-killing monster, but viewers never learn what happens to Yurtle the turtle.

After some intense social media lobbying from passionate fans, the official Stranger Things Twitter account was forced to clarify that Yurtle was safe and well.

Writers have also been pressed to explain why the Byerses' dog mysteriously disappeared in season two.

Stranger Things' third season isn't expected until at least the end of 2018.