Khloe even talked to one during a 2017 episode of "Keeping Up with the Kardashians."
While she was a guest on the show back on December 9, E! released new footage from the episode on Thursday, as Kim and the host talk about imaginary friends.
Though Kardashian never had one, she exposed Rob's hidden secret during the chat.
"My brother has, uh, I don't know if he still does. But he had, for a really long time, two imaginary friends," Kim revealed.
When asked if she remembered their names, Kim didn't hesitate. "Pablo and Ronald," she revealed. "My brother literally has talked about these guys like up until last year. He has one more but I can't remember his name."
While Kim blanked on the identity of her brother's other bestie, Khloe began "talking" to a third imaginary friend of his during a 2017 episode of "Keeping Up with the Kardashians."
After being ignored by her sisters, Khloe started to chat up "Cornelius," another one of Rob's imaginary buddies. During a phone call with his sister, Rob admitted he didn't "really see him as much anymore," adding that Cornelius had gone MIA after the death of his wife.
Watch that bizarre interaction below: