However, fans were not impressed.
"This friendship still weirds me tf out," one user commented while another wrote, "She's 41 and she's hanging around with 19-year-olds in swimming pools".
Kourtney, never one to let somebody get her down, replied, "Do you suggest a better place? I'm looking for ideas..."
However it wasn't only a couple of fans on Instagram who weren't feeling the friendship.
A long list of people have expressed how uncomfortable their friendship makes them on Twitter.
Kourtney and Addison's friendship goes back to January, when Kourtney enlisted YouTuber David Dobrik to help launch her son Mason's TikTok account.
In March, Dobrik introduced the two when he got Rae involved in Mason's TikTok.
"I met Kourtney through a friend, through David," Rae told The Tom Ward Show in June. "We surprised Mason, because Mason liked my videos on TikTok."
She added that "I kind of just stuck around and we got really close".
