Along with the throwback pic of the two of them below, Kourtney wrote "Bobby" and a heart.
Earlier this week, Khloe posted a throwback picture of herself and Rob with the caption, "#MyAce."
While Rob has chosen to stay out of the public eye for the time being, Kris Jenner recently reassured fans that he's doing all right. "He's doing alright, he's doing his best. He's not as into being on camera as much as the rest of us, but he's working on himself. He's gonna be OK..." she said during a recent appearance Maria Menounos' Sirius XM radio show.
We're not sure why Kourt and Khloe both posted messages with a day or two of each other, but it's sweet either way.