Backstreet Boys -- Surprise Gig at Balmain ... 'Cause Hot Models Want it That Way (VIDEO)

'90s kids in NYC rejoiced Tuesday night cuz the Backstreet Boys hit the stage for the Balmain x H&M fashion show.

Brian, Nick and those other guys performed some of their classics for the likes of Kylie, Kendall and Gigi Hadid. We're told Olivier Rousteing -- who designed the collection -- is a HUGE BSB fan and asked the group to close the show.

Our source says the performance was such a success Olivier and the Boys are in talks to work together on their upcoming tour.

Your move, 'N SYNC.