The reality stars fêted Khloé's on-again/off-again rapper boyfriend, who turned 30 on the 9th.
Khloé, 30, was particularly sexy in a slinky dress with hip-high slits up the leg, while sister Kim, 34, was more demure in an all-black turtleneck outfit.
Youngest sister Kylie Jenner wore her hair Ariana Grande-style, and a black mini-dress paired with silver necklaces and over-the-knee black boots.
Even though Khloé and French announced they were taking a break in September, the romance seems to have been rekindled.
Khloé shared a shot of the two of them on a stunning beach, captioning the image, "Happy birthday baby boy! In only a short amount of time we have created timeless memories. Happy birthday to a man who genuinely lives life to its fullest. "What's understood doesn't need to be explained" @frenchmontana I can't wait to celebrate life with you tonight! You deserve it!!"