It was BFFs only at Sofia Richie‘s big 21st birthday bash in Las Vegas — and Kylie Jenner was definitely a VIP. Sources dished to Life & Style exclusively that the two 21-year-olds seemed closer than ever at the event. The babes had a dance battle to the infamous Backstreet Boys track “I Want It That Way” at XS Nightclub at Wynn Las Vegas and had a total blast.

“Sofia and Kylie get along like best girlfriends. Super high energy. Kylie was celebrating her for her b-day, so when they were dancing she was playing around with her like a little sister,” the eyewitness gushed. “She picked her up and was swinging her around.”

Kylie Jenner

Along with her pals Stassie KaranikolaouYris Palmer and Victoria Villarroel, Sofia partied the night away with her close friend, who she has been developing a deeper and deeper friendship with over the last few months.

Sof was one of a few girlfriends to attend Ky’s luxe Kylie Skin girls’ trip to Turks and Caicos back in July, but the dynamic duo has been consistently gushing over each other on social media since May. And her boyfriend, Scott Disick, totally loves the connection.

“Scott is really happy that Sofia and Kylie have become so close again because it means that Sofia has been further accepted in the family,” a source previously dished to Us Weekly. But how does Scott’s ex and baby mama, Kourtney Kardashian, feel about all this, you wonder? She’s on the fence, if we’re being honest.

Sofia Richie
Denise Truscello / Getty Images

“Kourtney likes Sofia, but Scott is her ex and the father of her kids, so sometimes she feels that there should be healthier boundaries,” a source told Life & Style exclusively. “If Scott were to marry Sofia then that would be different. Maybe Kourtney is just feeling a little insecure because her kids love Sofia and now Kylie and Sofia are super tight.”

After more than two years together, it makes sense that the blonde beauty would be really settled into the Kar-Jenner fam. Despite the flashes of insecurity it must bring for Kourt, it’s clear Sofia’s closeness with Kylie and the crew is a good thing. Plus, it clearly makes for a great party.