Kendall Jenner, Gigi Hadid Go Crazy For the Backstreet Boys at Balmain x H&M Launch Party

Olivier Rousteing is on fire. On Tuesday night, Balmain’s creative director threw a Wall Street bash in honor of the brand’s H&M collaboration (it goes on sale Nov. 5) that didn’t just draw Kendall Jenner, Gigi Hadid, and co., but also reunited the Backstreet Boys, who jumped on stage in Balmain jackets to perform some of their biggest hits from the ‘90s. Seriously, we DIED. Also, the clothes were so hot, the fashion crowd barely knew what to do with them.

“I would normally wear a mini with a wool jumper,” said British model and TV host Alexa Chung, referring to her black, micro-sized blazer dress (or maybe it was just a blazer worn as a dress?). “But, I don’t think that would be Olivier-approved.”

“Olivier — you know his style — he wanted these super short, short dresses,” said H&M Design Director Ann-Sofie Johansson before the show. “We were like, ‘We have to lengthen them,’ so we had some fights about that.” But she felt OK with the compromise: “It’s so totally different than last year’s Alexander Wang — which was so sporty, urban, more street. This is glamorous, so detailed, so French.”

Indeed, what the collection might have lacked in fabric, it certainly made up for in opulence — and presentation. A raw, concrete former bank was transformed into a two-story metro terminal, with purple neon lights and a Plexiglas central staircase, where a troupe of dancers in I Dream of Jeannie ponytails and booty shorts kicked things off with some pretty crazy body contortions and, of course, twerking. Then the #BalmainArmy marched out, in their sharp-shouldered military blazers, intricately beaded wiggle dresses, silk Hammer pants, and thigh-high suede boots, which all looked fierce, but a little challenging. After going up and down the stairs multiple times, model Jourdan Dunn, wearing caged sandals and a white double-breasted satin pant suit, stuck her tongue out in exhaustion.

But then, as the lights dimmed and the last runway model made her exit, a voice from on high announced, “Ladies and gentlemen, the Backstreet Boys.” For a second, no one knew what was happening — Backstreet’s actually, for real, back? — when A.J., Howie, Nick, Brian, and Kevin emerged, looking sharp in their H&M jackets, singing “Everybody.” Editors scrambled over each other to get a prime spot on the balcony to Instagram their tween crushes’ (still killer) moves and scream their brains out. The Boys played their greatest hits, including “I Want It That Way” and “Larger Than Life,” which the whole thing kind of was.

“That was amazing,” exclaimed Jonathan Cheban, a Keeping up with the Kardashians regular, as he made his way to the frenzied showroom, where guests could shop the collection early. “Best show I’ve ever seen — better than anything at Fashion Week.” He then got to work finding one of those men’s blazers — any of them — in his size.

“I loved the colors,” said Alek Wek, herself in a beaded magenta calf-length Balmain x H&M shift. “When I saw this dress on the hanger, I was like, I don’t know, but I put it on, and it was so comfortable — I never would have expected that. And, I love Olivier is giving Balmain to all these people who couldn’t otherwise afford it. Like, my niece, she’s a university student at Cambridge, she’s like, ‘I’m going to wait in line first thing when it opens.’”

She better get there early, if last night’s shopping event was any indication. Whether it was the high from the performance, the flowing booze, or Rousteing’s dizzying clothes themselves, the sales floor was pandemonium. Victoria Secret model Alessandra Ambrosio, tired of waiting for a fitting room, began to strip and try on garments behind a rack. “Can’t you see I’m trying to shop,” snapped Coco Rocha when asked for her opinion about the show, as she grabbed an armful of the more bedazzled numbers. A military olive-green shirt in the men’s section was so coveted (by both genders) that editors would hover as other women would try it on, pouncing on it the second it was abandoned. Joan Smalls — who made a beeline for the men’s department, eyeing some of the T-shirts and threadbare tank tops — was reprimanded by a security guard for cutting in line at check-out.

But Rousteing — fashion’s great democratizer — was loving it. “It’s so fun seeing everyone go crazy,” he laughs. “And having the Backstreet Boys was a dream come true. They’ve been an inspiration for so long; I love them.” As for his after party plans, the designer, who taught Jenner to twerk for H&M’s campaign video, silently lifted his arms, did some robot-like moves and shimmied over to his army of gal pals, ready to dance the night away.