So there wasn’t a model dance-off like snippets from the Balmain x H&M campaign video hinted, nor did Kanye West — who starred in Balmain's Spring 2015 campaign, and is brother-in-law to Creative Director Olivier Rousteing’s muse, Kendall Jenner — take the stage. 

Instead Balmain and H&M surprised crowds of fashion insiders Tuesday night with a post-fashion show performance by none other than '90s boy band the Backstreet Boys.

Why? Because Rousteing, age 30, is a big fan of the group. "Having the Backstreet Boys was a dream come true," he told Yahoo Style. "They've been an inspiration for so long." 

He’s not the only fan. Editors and models, including Jenner and pal Gigi Hadid, sang along to hits like “Larger than Life” and “I Want it That Way.”

Following an epic, and never-ending, fashion show — which started and ended with dancers voguing — models strutted in looks on a bi-level runway. This involved lots of walking up and down stairs.

The real show, however, was down in the basement, where showgoers were allowed to shop the glamorous collection of Rousteing's greatest hits before it goes to stores on November 5.

Earlier in the day during a press confrence, Rousteing said he chose to recreate some of his succussful signature items because he wanted to make couture afforadable. "I remember watching shows and feeling frustrated wishing I could afford this piece. So I anted to make it happen."

Surprisingly, it wasn’t the peacocking "Dynasty-" esque beaded jackets or blingy tops he's known for that sold out first, but rather, the subtle and tailored menswear.

"The menswear is exactly who I am," said Rousteing. "It's my closet."