WATCH: Venus works out with Dimitrov on Instagram Live

Venus Williams, better known as Coach Venus, has been in the Instagram Live house for a week now. From her Jupiter, Fla. home, the 38-year-old hosts daily live workouts at 12 p.m. EST.

On Tuesday, she kicked things up a notch by working out with a special guest: Grigor Dimitrov.

Fans went wild for the celebrity cameo, and Venus played right into it.

"Being one of the biggest heart throbs on tour, how do you keep a six-pack?" Venus asked Dimitrov. "If you want to have donuts, do you feel guilty that you’re letting your fans down?"

"Because I’m having a donut?" Grigor replied. "I think it’s important to have indulgences. You work hard, you just gotta enjoy a little bit. Plus, I’m still trying to work on my six-pack every day. I wake up, exercise. My diet has changed so much the past three, four years. I cherish those moments. I don’t have them all the time.

"I treat my body like it’s my temple. Sometimes, you need to let one slide."

"Six-pack abs day: maybe you can lead that one day," Venus said. "Can you give us a sample of the kind of results we should expect?"

The Bulgarian played along, and flashed his abs.

With the banter behind them, the two champions got to work, jumping rope, doing lunges, executing shadow stroke jumps and racing through footwork drills. They ended with some stretching chatter.

"I think it's so personal. I stretch a couple times a day," Dimitrov said.  It’s how you feel your body to be honest. It also depends on the time you stretch."

"Depends on the kind of day I’m having, but I’d say a couple times," Venus said. "I find when I stay looser, I warm up quicker. You feel just so much better in life, for me."

Expect a lot more online from Coach Venus, maybe with more surprise guests.