ET caught up with the reality star "momager" at The Daily Front Row’s Fashion Los Angeles Awards on Sunday night, where she explained Khloe didn't make it to the big 2-9 family celebration because of work and illness.
"She was working and then she was sick and just had a crazy... yeah," Kris said. "I'm not even sure if she was working in or out of town. It's just so crazy."
And although she couldn't make it, Khloe wish her brother happy birthday with a throwback photo on Instagram, writing, "Happy birthday to my ace @robkardashian!!! Forever my best friend!! I love and adore you!!."