When the cat's away, the boyfriend will party with his old flame!

James Harden and Amber Rose were both caught partying at 1OAK in Hollywood last night, and the basketball star's girlfriend Khloe Kardashian is probably not going to be happy about it! After all, the Houston Rockets star reportedly used to hook up with Amber!

Making things even worse, the timing seems a bit sneaky! The E! starlet is in New York for fashion week with the rest of the Kardashian clan, and it seems unlikely she OK'd this hangout. The reality star might want to think twice about her plans for the future with the bearded lothario.

"James is in love with Khloe and is really all in with the relationship with her, as well. He really believes they will be married, but he doesn’t want to pop the question because she is apprehensive about marriage with the fallout from Lamar [Odom]. But they have definitely talked about babies and they want one with each other. But Khloe knows that James wants an NBA Championship first. that’s his first priority," a source dished to Hollywood Life.

Someone's going to have some explaining to do when his girlfriend gets home!