October 26, 2017 08:46 AM

Kourtney Kardashian just made her mark in the fashion world — and she did it with the sweetest support!

On Wednesay, the Keeping Up with the Kardashians star, 38, celebrated her first solo fashion collaboration with PrettyLittleThing at Poppy in West Hollywood, where she was joined by her younger sister Kendall Jenner – and boyfriend Younes Bendjima!

“Kourtney, Kendall and their group of girlfriends all arrived around 10 p.m., and headed straight to a VIP area next to the deejay,” a source tells PEOPLE. “Younes showed up not too long after.”

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“She looked like she was having a blast the entire evening,” the source adds of the eldest Kardashian sister, who rocked a black sequin mini dress from her collection for the occasion.

“She was smiling the whole night, laughing and chatting with her girlfriends. And as soon as Younes showed up, the two kept close and stayed next to each other,” shares the insider. “They were whispering in each other’s ears, taking photos, and at one point, she adorably draped her leg over his.”

Younes Bendjima and Kourtney Kardashian
Splash News
Kendall Jenner
Splash News

An hour later, Sean “Diddy” Combs got on stage with Kourtney and gave her a congratulatory shout out before he treated partygoers — which included Fuller House star Lori Loughlin, her daughter Olivia Jade, Teyana Taylor, Wiz Khalifa, Christina Milian and Adrienne Bailon, amongst others—to a surprise performance.

“Kourtney was sitting on Younes’ lap for part of Diddy’s performance. It was adorable,” said the source. “They looked really happy.”

RELATED VIDEO: Kourtney Kardashian and Boyfriend Younes Bendjima Share Steamy Kiss at Paris Soccer Game — But He Appears Distracted

The group, minus Jenner who left earlier in the evening, headed out once Diddy finished his performance just after midnight.

Kardashian previously told PEOPLE that she received a few opinions from her sisters when she was designing her 32-piece “Studio 54, old Hollywood and ’70s-inspired” collection.

“I see my sisters almost every single day, so while I was designing the collection, if I was going over fabric swatches and they were sitting next to me, I would ask their opinion, like confirming, ‘This is really a good dress, right?’ to just kind of get their stamp of approval,” the mom to Mason, 7, Penelope, 5, and Reign, 2, said.

Kourtney’s line with PrettyLittleThing is available now.

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