Also excited to be hanging out with the former Cheetah Girl, Kourtney shared another photo of the trio, writing: "Reunited best friends lol."
This rekindled friendship between Bailon, 32, and the Kardashian-Jenner sisters comes less than a week after Blac Chyna shaded Kylie -- who is dating Tyga, the father of the 27-year-old model's son -- for allegedly stealing her cooking show idea.
A few days later, Rob posted a NSFW message that seemed to be in support of his girlfriend. "When the p**y so good but your family don't like her," the 28-year-old wrote. "So you drop your family and become an orphan."
However, Bailon has not always been so chummy with her ex's famous family. In the summer of 2014, she outright slammed the Keeping Up With the Kardashian stars to Latina magazine.
"To be stuck with that Kardashian label, that was so hurtful to me and to my career. I probably realized that too late -- not that it would've affected my decisions in terms of who I dated, but it would've affected my decision to appear on the show," she said. "At the time, I didn’t think anyone would even care. To this day, people will still say, 'You ruined Rob's life!' and I'll think, 'Damn, I was still playing with Barbie dolls when I met him.'"
Kim Kardashian defended her brother at the time, tweeting: "Funny how she says being with a Kardashian hurt her career yet the only reason she has this article is because she is talking about a Kardashian. #LetItGoooooLetItGoooooo (FROZEN VOICE)."