'Stranger Things' Flashback: 12-Year-Old Millie Bobby Brown Adorably Reacts to the Demogorgon! (Exclusive)

We’re traveling into the Upside Down for this Throwback Thursday!

We’re traveling into the Upside Down for this Throwback Thursday!

Stranger Things' highly anticipated third season is almost here and -- just like the rest of the internet -- we’re currently counting down the seconds until we’re reunited with our favorite monster-hunters in this awesomely ‘80s drama.

But before fans first binged their way into a parallel universe and rediscovered their love of Eggo Waffles, the stars of Stranger Things were unaware that they were about to be part of one of the biggest TV shows of the decade.

ET first sat down with 12-year-old Millie Bobby Brown and actor David Harbour in March of 2016 -- four months before the series premiered on Netflix -- to get the inside scoop straight from the actors who were, unknowingly, on the brink of superstardom.

"Don't be scared," Brown, who plays psionic Eleven, said when asked what fans should know before tuning in. "Don't be scared. It's not scary."

"It's totally scary!" Harbour interrupted while Brown playfully rolled her eyes.

"It's a great character piece like these shows like The Sopranos or Breaking Bad. It has great characters, it has great scenes, it has great dialogue -- and then there's monsters too." Harbour continued. "And there's other realities, so that's really exciting because I love both those genres and it's not just one or the other. I think it's unlike anything else I've ever seen."

Iconically, Stranger Things introduced fans to The Demogorgon, a predatory humanoid creature from a dark parallel universe called The Upside Down.

In the season one finale, Eleven faced her fears and triumphantly obliterated the monster, but off-screen, Brown admitted that she was unfazed when she first came face to face with The Demogorgon.

"I fear nothing," the pint-sized actress boasted with a laugh.

Meanwhile, Harbour confessed that he was genuinely creeped out by the practical effects suit the Demogorgon actor wore on set. "That thing is scary!" he exclaimed. "I mean, the guy was sort of in the suit, so I saw the guy, but it's this horribly disfigured thing with long, otherworldly limbs and the face does something that you don't want to, you never want some face to do, right?"

Brown admitted that she was "surprised" that her older co-star was startled by the creature.

"I'm not very scared of things like that. I mean, I'm scared of, like, ghosts and stuff, but monsters? They don't really scare me," she said. "I think with the monsters, it's that sort of mystery. You don't really know what it's going to do."

"That's true," Harbour added. "You know it's going to hurt you, you just don't know how… Honestly, the best thing about the monster is how little you see it."

"Yes!" Brown agreed at the end of our interview, "That's what makes it scary."

We hope you've enjoyed this blast into Stranger Things' past and be sure to keep it locked to ETonline for all the latest secrets straight from the stars as we gear up for season three of Stranger Things which drops Thursday, July 4 on Netflix.