Gigi Hadid Has Star-Studded 21st Birthday Bash -- Both Taylor Swift and Ex John Mayer Awkwardly Attend Along W

The big 2-1! Gigi Hadid rang in her 21st birthday on Thursday night with a blow-out, celeb-filled bash at The Nice Guy in Los Angeles. The supermodel strolled into the celebrity hotspot with pals Taylor Swift, Kendall and Kylie Jenner, Khloe and Kourtney Kardashian, Hailey Baldwin, Lily Aldridge, Jaden Smith, Lenny Kravitz, Ashlee Simpson, Evan Ross, Hailey Steinfeld, and Naomi Campbell.

The birthday girl wore several choker necklaces with a black satin tank top and white booty shorts. She paired the look with thigh-high cutout boots, which she showed off on Snapchat.

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Hadid’s A-list pals pulled also out all the stops when it came to their outfit choices. The platinum-blonde Swift rocked a one-shoulder, sequin-covered mini-dress while Kendall wore a see-through bra, which her sister Kylie revealed in a NSFW Snapchat featuring her nipple ring.

Khloe and Kourtney both went above and beyond to attend the soiree after Kourt revealed on Snapchat that she’s been sick, and Khloe added that she fell down her stairs, injuring her leg.

“I need to know if this is thirsty,” Khloe asked her fans on Snapchat. “So last night I fell down my stairs and I really hurt my leg. My leg is really swollen now and it’s kind of hard to walk, but I’m supposed to go to a birthday party with me and all my sisters and I have FOMO. I really want to go, but is it so thirsty because my leg hurts and I probably should be icing it and probably should be staying home?”

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Thirsty or not, Khloe went out with Kourt in matching black jumpsuits, jamming to Beyonce’s new Lemonade album in the car.

The party’s guests seemed to be having a blast, posing for pics in the photo booth. Even Gigi’s mom, Yolanda Foster, attended the bash, snapping a photo with her daughter, Swift, and fellow model, Aldridge.Gigi's father, David Foster, also attended the event, but did not interact with his ex, a source tells ET.

Interestingly, Swift's ex-boyfriend, John Mayer, also attended Gigi's party, though there's no indication that the former flames interacted. 

Gigi’s boyfriend, Zayn Malik, also attended the event, a source tells ET, arriving late and sitting at Gigi's table. The pair previously celebrated her birthday at Disneyland last weekend. Gigi’s actual birthday was on April 23.

She will continue the celebrations with another party on Saturday at the grand opening weekend of Intrigue nightclub at the Wynn in Las Vegas.