Karan Donna who Halsey is.

A performance by Halsey was the big attraction at DKNY’s blowout 30th birthday bash Monday, but Donna Karan seemed confused as to who the hot singer is.

“Who is Halsey? Is that Halsey?” Karan asked Page Six, pointing to a guest who was definitely not the star. Karan added, “I think my granddaughter does [know who she is]. I’m sure she’s great.”

Following a set by DJ duo the Martinez Brothers, Halsey was introduced by model Cara Delevingne — who arrived with girlfriend Ashley Benson — to an enthusiastic group who clearly knew her, including Kendall Jenner, Suki Waterhouse, Luka Sabbat, Offset, Winnie Harlow and Alessandra Ambrosio.

“It’s good to be in Brooklyn,” Halsey told the crowd at St. Ann’s Warehouse. “Five years ago you motherf - - kers would’ve been too cool to talk to me.”

Karan left the brand in 2015, and it was sold by LVMH in 2016. She now focuses on her line/nonprofit Urban Zen. Later in the night, Jenner, along with Bella Hadid, was spotted at Avenue, where Parisian nightclub L’Arc was doing a pop-up. Jenner is not walking in any shows this season, telling Vogue that she’s scaling back her workload: “It’s a lot more mellow to just go.”