Nothing marks the rise of a starlet into the upper echelon of Hollywood quite like a front-row appearance at New York Fashion Week.

Just ask Millie Bobby Brown, the 13-year-old breakout star who made her Fashion Week debut last fall at the Coach show, just two months after Netflix’s “Stranger Things” turned her into a boldface name. Last week, she solidified her It-girl status with a front-row seat at the Calvin Klein show. Ladies and gentlemen, Millie Bobby Brown has arrived.

With an Emmy nomination in the category of Best Supporting Actress in a Drama Series, she’s one of the youngest stars to ever receive a nod. It’s a rare feat for a kid actor — “The Cosby Show” star Keshia Knight Pulliam was nominated at age 6, but Roxana Zal is the youngest winner at age 14 for the TV movie “Something About Amelia.”

It says a lot about Brown that she was recognized alongside the likes of Ann Dowd and Samira Wiley of “The Handmaid’s Tale,” Uzo Aduba of “Orange Is the New Black,” Chrissy Metz of “This Is Us” and Thandie Newton of “Westworld.”

Born in Marbella, Spain, Brown was the third of four kids born to parents Robert and Kelly. The couple moved the family to the UK when Millie was 4, then to Orlando, Fla. when she was 8. It was in Florida that Brown began taking performing-arts classes on weekends, and was spotted by an agent at a showcase who suggested that she and the family relocate to LA.

The first role she landed was as the younger version of Alice on ABC’s 2013 series, “Once Upon a Time in Wonderland.” Showrunner Zack Estrin was so impressed with her brief work in the pilot, he had her written into a later episode specifically to bring the young actress back.

“She walked on the set like she was born on it. She was the most confident child I had ever seen,” Estrin tells The Post. “I remember turning to her parents going, ‘You guys better get ready.’ It was obvious even then . . . I had to let them know they had a unicorn.”

Estrin tried to get Brown for his next show, “The Whispers,” but she was already booked for a BBC series, “Intruders.” Then came the big one — the role that would change Brown’s life forever.

“Stranger Things” casting director Carmen Cuba first watched Brown’s submitted audition tape, and then had her read via Skype for the sci-fi show’s pivotal role of Eleven, a mysterious young girl with peculiar powers. Cuba recalls that Brown’s American accent was so good, she didn’t even realize she was hiding her normal British accent until the end.

“As herself, she was a bright, shining light of a kid filled with enthusiasm about playing and being imaginative, but in the role she could shut that off and go really deep and intense,” Cuba tells The Post. “Having a kid who was naturally similar to Eleven in darkness and intensity would have been hard, because nobody wanted to feel like we were torturing someone so young and still developing emotionally.”

The movers and shakers of Hollywood agreed that Brown had something special — the role earned her a shared SAG Awards ensemble win and an individual nomination, and the Emmy nod soon followed.

The second season of “Stranger Things” won’t bow on Netflix until Oct. 27. A role in the next “Godzilla” movie is forthcoming, but Brown hasn’t appeared in any films or shows since her big break. No problem; she’s stayed busy with front rows, red carpets, editorials and ad campaigns. She signed with IMG Models in February and booked work with Converse and a big gig with Calvin Klein as the face of their made-to-order line.

Like former “Mad Men” star Kiernan Shipka before her, she’s the superstylish teen we all want to be. That’s thanks in part to a distinct look cultivated by tastemakers such as Justin Bieber’s stylist Karla Welch and Thomas Carter Phillips, who works with Emmy Rossum.

“She looks vintage and exceedingly sophisticated for a 13-year-old,” explains stylist-to-the-stars Robert Verdi, comparing her look to that of ’60s icon Twiggy. “She also has an intense personality in an image, which is an X factor that nobody understands.”

Still, her mother keeps her in line. “My mum helps me look my age,” Brown recently told Teen Vogue. “Like, I can play with makeup, but I can’t go crazy. She’s also like, ‘You can’t wear that crop top.’ ”

“Most kids do what their friends are doing, like a domino effect,” she said in the same interview. “But I do my own thing.”

She’s talking about clothes, but she might as well be talking about her promising career — midriff be damned.