"Spotted these fools on the morning workout," he captioned an Instagram pic of the youngest Jenner sibling and the rapper.
It appears to be the summer of health for Rob. Earlier this month, Kim Kardashian revealed that she was working out with her 28-year-old brother. "Just went on the hardest hike ever today with @robkardashian," she tweeted on August 14.
Kim also tweeted on Tuesday: "Rise & Grind! Workout time!!!!! With @robkardashian."
"Rob lives with me now and I wouldn't have it any other way. I love having him with me," the 31-year-old reality star told Complex magazine. "He's going through a hard time now and it's behind gates. With this crazy lifestyle you have to think of places where you can still have your freedom."