“I’ve never seen that in a child actor.”

It’s almost a mantra for anyone who’s worked with Millie Bobby Brown.

Whether it’s “Stranger Things” executive producer Matt Duffer praising her on-set technical knowledge, co-star David Harbour extolling her emotional intelligence or casting director Sarah Finn explaining why she selected her for the next installment in the “Godzilla” film franchise — even the most seasoned industry pro marvels at the young actor’s preternatural ability.

Zoey Grossman for Variety

Brown, now just 13, has never trained professionally as an actor. Never gone to acting school. Never taken a class. She simply decided at age 8 she wanted to be on-screen, and her parents obliged, moving her and her siblings from Bournemouth in England to Orlando, Fla., to allow her to pursue her dream.

“It was like a bug,” she says. “I know this sounds crazy, but once I find something I want to do, nobody’s stopping me. If I don’t know how to sew, and I really had that passion to sew, that’s it, I’m going to sew. That’s also with acting. So here I am.”

Her path to stardom wasn’t immediate: She secured a few guest star spots here and there, in shows like “Once Upon a Time in Wonderland,” “Modern Family” and “Grey’s Anatomy.” She got turned down for “Logan,” which eventually went to Dafne Keen. But it was the role of Eleven in Netflix’s sleeper hit that catapulted her to fame.

“I felt at one point I couldn’t do it [anymore], but then I got this and everything changed,” she says over a mid-afternoon soda break at the London hotel in West Hollywood. Now, “acting is like breathing to me.”

To say the past year of her life has been a roller coaster would imply that there have been dips. In fact, it’s been nothing but a steady climb since the July 2016 bow of “Stranger Things.” Her Instagram followers ballooned from 25 to 4.2 million; the cast won best ensemble at the SAG Awards and best drama at the PGA Awards; and she claimed her own trophy at the MTV Movie & TV Awards for best actor in a TV show, with an emotional acceptance speech that won her even more accolades for its honesty. And with season two of “Stranger Things” now streaming (it debuted Oct. 27), she just wrapped production on the next installment of the “Godzilla” franchise opposite Kyle Chandler, Vera Farmiga and Thomas Middleditch. (“You’ll find out in two years,” she jokes about her secret role in the film, which is slated for a 2019 release.)

Then there’s that Emmy nomination for supporting actress in a drama. “It was a true honor and privilege to be representing the young generation,” she says. Although she went home on Emmy night empty-handed, she took things in stride, happy to simply enjoy the evening out with her merry band of co-stars.

“I’m leery of blowing too much smoke up her already well-filled smoke ass,” says Harbour, who plays Chief Hopper on the Netflix hit. “Because I do feel that when I’m in the nursing home, I would like to be able to watch movies with her in her 30s and have her become Meryl Streep. She has the potential for that to happen.”

It was all about the Look.

Fans of “Stranger Things” know it well: when Eleven lowers her chin and glares defiantly at whoever — or whatever — is in her path.

It was in her audition for the role that she came up with that intense laser-beam stare — and nailed the part. She was 11 at the time.

Zoey Grossman for Variety

“I’ve never forgotten it, because it was so intuitive,” recalls executive producer Shawn Levy. “That this little person had such fierce power — that’s what took me aback. That same day the Duffers [brothers Matt and Ross, who created the show] and I knew she was the one.”

In the “Stranger Things” universe, Eleven — so-called because of the tattoo she wears — is a product of psychological experiments by Dr. Martin Brenner (Matthew Modine) that infused her with telekinetic abilities, among other supernatural powers. Because of her years of isolation under Brenner’s watch, her vocabulary is rather limited. (One fan counted: Her dialogue amounts to just under 250 words in the whole first season.)

Brown wasn’t intimidated by the role of Eleven being mostly nonverbal. “You can talk with your face,” she says matter-of-factly. “It’s very easy for someone to say, ‘I’m mad. I’m sad. I’m angry.’ I have to just do it with my face.”

Nor did she mind shaving her head. Brown’s parents were more against it than she was, but it helped that “Mad Max: Fury Road” was out at the time. Matt Duffer recalls persuading her with the argument “Doesn’t Charlize look badass? You’re going to look badass too.”

What did cause a bit of on-set drama was The Kiss — the moment when Mike (Finn Wolfhard) and Eleven smooch in the season-one finale. For all of her remarkable self-possession, the little girl that’s still in Brown reveals itself when she recounts the moment — her first kiss ever. “It was a strange experience. Having 250 people looking at you kissing someone is like, ‘Whoa!’” she says.

Further complicating matters, it seems there’s some debate over whether it was Wolfhard’s first smooch as well. “He says I wasn’t, but I definitely think I was,” she says. “I think he was just trying to be cool.”

As for how those awkward teenage moments play out in the second season, “No comment,” say the Duffer Brothers.

“My character’s just so, so perfect for me,” says Millie Bobby Brown. “I definitely think that we relate to each other a lot.”

Courtesy Netflix

The Duffers, who write, direct and executive produce the series, have gotten a front-row seat to Brown’s talents. The role of Eleven was always central to the show’s plot — it’s with her help that the boys rescue their friend who’s vanished into the Upside Down — but with Brown on board, the storytelling options have blossomed.

“We have yet to give her something that she’s unable to do,” says Matt Duffer. “I can throw this girl an incredible fastball, she’s going to hit it. It’s like a singer who can hit any note. Her range is just absolutely incredible. I have yet to see any limits to it.”

He compares her to Tom Cruise in her keen perception of how the camera works — and how to use it to her advantage. “She’s four years away from knowing what millimeter lens she’s on and how she should adjust her performance accordingly,” he says. “She’s not there yet, but it’s right around the corner.”

Ross Duffer recalls the scene in season one where Eleven is being dragged down the corridor shouting “Papa!” at Brenner. Even the crew stopped to marvel. “That was when we realized, as good as she is, she’s even better than we thought,” he says. “We can push her to all these intense and emotional places.” They take her even further in the second season (there’s an epic finale showdown), and report she “knocks it out of the park” every time.

And the critics agree: “Brown’s ability to summon emotion is as impressive as her character’s ability to walk between worlds,” writes Variety’s Maureen Ryan.

As Brown heads into her teenage years, the question is whether she can avoid that curse of child stardom that has plagued so many before her. “Everyone from Tennessee Williams to Sarah Paulson has warned of the perils of early success,” says Harbour. “There’s a piece of me that’s very protective of her and feels that we should all let her be brave and brilliant and turn our eyes away and not give her so much attention.”

Levy says her close family ties give her a “fighting chance.” She’s surrounded by her parents, as well as her 23-year-old sister, who’s usually on set with her and travels with her. And if all else fails, there’s Harbour: “I tell you what, she’s got me. And I’m the biggest curmudgeon around.”

Brown has purposely made her U.S. home in Atlanta, far from the crush of Hollywood, where she jokingly complains every waiter is an actor. “I feel like Hollywood is just a place where everything’s going so fast,” she says. Georgia, she says, is “calm, peaceful, beautiful.” There she can keep herself “grounded for my family and my home and my friends.”

She’s been flooded with advice, but the one thing she’s retained is this: “To live in the moment and to make mistakes is a big part of being a person,” she says. “I’m still just a kid. I’m 13, and making mistakes is OK.” So if a spoiler slips (no such luck!) or she says something wrong on Twitter, so be it.

“We knew Eleven was a cool character on the page — it took the magic of Millie to make it this culturally iconic figure.”

Executive Producer Shawn Levy

She’s trying to hold on to some vestiges of her childhood and not rush headlong into adulthood, despite all the magazine cover offers coming her way. “I don’t like showing off my skin,” she reveals. “If I’m in a photo shoot and they’re like, ‘Can you wear a crop top?’ I’m like, ‘No. No, not yet.’ When that day comes I’m going to be, like, 18.”

She plans to spend her hiatus doing charity work. “I just want to focus on helping other people,” she says. “Working with Unicef is a really big dream of mine.”

And while she’s content to focus on acting, her other passion is singing — just watch her impressive rap to Nicki Minaj’s verse on “Monster” on YouTube. As with acting, she’s never trained. “It came to me naturally,” she says.

Even more remarkable, Brown is deaf in one ear — she was born with partial loss of hearing, and then her hearing faded away after years of tubes. So she can’t fully hear herself perform, but no matter. “I just started to sing, and if I sound bad I don’t care, because I’m just doing what I love,” she says. “You don’t have to be good at singing. You don’t have to be good at dancing or acting. If you like to do it, if you genuinely enjoy doing it, then do it. No one should stop you.”

Season one of “Stranger Things” ended with Eleven sacrificing herself to the Demogorgon who’s been terrorizing the town. But there was never really any question that Brown would return for season two. (And we did see Harbour’s Chief Hopper leaving those Eggos, her favorite snack, in the woods.)

“Once we realized [‘Stranger Things’] was going to be multiple seasons, Eleven was such the heart of the show we had to keep her,” says Ross Duffer.

Brown says she knew she was coming back and is relieved she finally gets to talk about it, since she had to keep it a secret even from her family. But she’s been well-trained in the art of avoiding spoilers (“I’m a pro at this now,” she says when her publicist hands her talking points for an upcoming panel), and ahead of the premiere, she refuses to reveal how or why Eleven returns.

“It’s really twisted and just perfect,” she says cryptically.

“We thought she was special, but once we saw what she was capable of in front of the camera, it just blew us all away,” says Ross Duffer, who created the show with brother Matt.

Jackson Lee Davis/Netflix

Season two, which picks up a year later in 1984, probes more deeply into Eleven’s backstory. “We wanted to delve more into her past and how she ended up where she ended up,” says Ross Duffer. “It’s an emotional journey for Millie and her character to see where she came from. The first season was a fish-out-of-water, ‘E.T.’ story for her. This season we wanted to give her more of an arc and a journey.”

Adds Matt Duffer, “I think people are really going to respond to her storyline.”

We find out more about not just her mother but her connection to Brenner, the man she calls her father. “Without Papa, Eleven wouldn’t be Eleven,” says Brown. “Everybody thinks he’s evil, but he was a big part of Eleven’s life. He was her Papa.”

But her true father figure is Harbour’s Chief Hopper. “They’re both such strong, oddball characters,” Harbour says. “We wanted to fit this feral cat of a little girl, wise beyond her years, who also has these supernatural abilities, with this very broken man who’s got issues about his own parenting abilities. There’s some connection that Hopper understands about the reemergence of Eleven that very much comes into play in season two.”

This time out, Eleven has more hair (“We let it grow out, as much hair as was able to grow from season one to season two,” says Ross Duffer) and more dialogue. (Among her new favorite words: “Mouth-breather.”) “She’s not speaking as if she was raised and lived in the regular world her whole life, but it’s a more verbal performance,” says Levy. “But in spite of more written dialogue in season two, Millie’s more powerful moments remain the ones without words.”

And there’s a new girl in town, challenging Eleven’s role as the lone girl in the gang of boys: Sadie Sink plays Max, a skateboarding tomboy with “a complicated history and a suspicious streak.” And though their characters may not exactly bond immediately, off-screen is a different story: Brown’s Instagram is filled with photos of her and Sink, whom she calls a “sister.” “I loved having a new girl on the show, because it’s nice not to be surrounded by boys,” Brown says. “One girl is just perfect.” Echoes Sink, “Me and Millie automatically clicked because we were the only girls in the group.”

Spoiler alert: There’s one moment this season that had Brown in tears. “I cried for hours actually after that, because it was just so sad,” she says.

All involved acknowledge the pressure of living up to the nearly impossible expectations of the sophomore season. “I don’t believe in resting on your laurels,” says Harbour. “I think the purpose of artistry in some degree as opposed to entertainment is to be one step ahead of your audience. Give them what they might not know they need as opposed to just rehashing the hits. So from very early on, the first scripts we were like we’re going to take some chances that hopefully will pay off. It might upset some people. But it was exciting to be a part of it.”

Zoey Grossman for Variety

Brown’s ties to the boys — Wolfhard, Noah Schnapp, Gaten Matarazzo and Caleb McLaughlin — seems unbreakable. Their palpable on-screen chemistry translates off set, where they spend much of their free time together — at Six Flags, on sleepovers, on giant text chains that the Duffers occasionally get caught on. (“That’s not so fun,” sighs Matt Duffer.) “They’re close and they’re going to be bonded in some way for life, and I think they realize that,” he says.

At the London, Brown can’t resist looking over with a tinge of jealousy as the boys run around nearby, on a break from a tutoring session. “I know the true boys, and they know the true me,” she says. “We like to be as private as we can.”

Wolfhard calls her “one of the best actresses I’ve ever worked with.” “If you put something on her shoulders, something big or a big scene, she’ll figure it out,” he says. “She can handle pressure very well.”

Schnapp says he’s grown closer with Brown in the second season. They’ve become prank buddies — they called the show’s costume designer and told her her wedding had to be canceled — and he’s especially fond of her ATV. “We ride it all the time and watch scary movies together,” he reports.

As luck would have it, the production of “Godzilla” was in Atlanta. She bonded with director Michael Dougherty over a mutual interest. “I have such a passion about animals and he did as well, and I felt like we just immediately connected,” she says. “I was like, I need to work with him. I need to.”

She points out, though, that she’s going to be 15 when the movie finally comes out. “I’m going to see my 13-year-old self and be like, ‘Why did I do that? Why did I blink at that specific time?’” she says with a sigh. “I’m a perfectionist, so I don’t like to watch my work.”

Millions would beg to differ.