Kourtney Kardashian, 36, and Kylie Jenner, 18, hung out recently with Adrienne Bailon, their brother Rob Kardashian's ex-girlfriend.
"Reunited best friends lol," Kourtney said on Instagram Sunday, alongside a photo of her and Bailon, 32, sitting on Kylie's lap.
"Cause we are sistersss," Kylie wrote, alongside another pic.
Bailon also posted Kylie's photo, posting three heart emojis.
It was revealed last month that Rob, 28, is currently dating Blac Chyna, 27, who shares a 3-year-old son with Kylie's boyfriend, Tyga, 26.
Bailon, co-host of The Real, dated Rob for two years before they broke up in 2009. She appeared on Keeping Up With the Kardashians. Rob admitted to being unfaithful to her in a 2010 episode.
In 2014, Bailon stirred the anger of Kim Kardashian, 35, and Khloe Kardashian, 31, after she talked about her and Rob's relationship in Latina magazine. She said getting "stuck with that Kardashian label" was "so hurtful to me and to my career."
Bailon later told E! News, "I never meant any harm with anything I said" and called Rob's sisters "great girls" and all the family members "amazing people."
In October, Bailon denied rumors that said she and Rob had reconciled, adding, "I think Rob is an amazing guy."
Meanwhile, things appear to be getting serious between Rob and Blac Chyna.
He has in recent weeks appeared more often in public, often with her, after largely keeping out of the public eye for more than a year as he battled personal issues, mainly weight gain. He was hospitalized briefly and diagnosed with diabetes in January. Blac Chyna appears to have inspired him to get healthy—the two have hit the gym together.
Rob also recently acquired a $2.285 million house near his family, with mom Kris Jenner's help, and his girlfriend has been helping him get it ready.
"They both have discussed moving in with each other," a source told E! News last week. "They feel this is a fresh house and a fresh start for them."