Kim Kardashian Reveals the Skinny on Her Waist Size: 24 Inches

Kim Kardashian's waist is tinier than ever, she revealed Monday as sister Kourtney Kardashian gawked at her hourglass figure.

The 37-year-old Keeping Up with the Kardashians cast member shared a video from the sisters' book club meeting on her app Monday, but before the discussion turned to the newest literary selection, "Embraced by the Light" by Betty J. Eadie, Kourtney remarked on the size of Kim's waist.

"I can't take your hips seriously right now," Kourtney said to Kim. "Because your waist is so small and your hips are so big."

Kardashian hair stylist and best friend Jen Atkin then asked Kim for her measurements, at which point the KKW Beauty CEO had Chrissy Teigen guess. The model ended up guessing 23 inches, which was pretty close to reality.

"24," Kim said in reply.

"24? That's insane," Atkin added.

"It's never been 24 ever in my life," Kim said, adding that her hips are 39 inches.

After giving birth to her and husband Kanye West's son, Saint West, in Dec. 2015, Kim began the Atkins Diet and got back on her workout grind to lose the 70 lbs. she had gained during her pregnancies with Saint and daughter North, 4.

But in the last year, as documented on the family's E! show, Kim has taken her fitness journey to a new level with trainer and bodybuilder Melissa Alcantara.

"Kim told me, 'I love my body. I love the way it looks and I love my hips,' " Alcantara recently told PEOPLE. "She just wanted more muscle. She wanted bigger hamstrings, which accentuates the entire leg. And she wants those cut arms and abs!"

Alcantara says Kim now works out with her six days a week beginning at 6 a.m., and the two focus on a different area of the body every day.

"Kim has been getting some really nice results, like with her triceps!" Alcantara said. "She can't believe how much has changed over the last few months. And when you're in this deep, it's hard to go back. She just keeps it up."

The trainer added that Kim's goals have changed as far as her fitness and body.

"She didn't want to be skinny. She wanted to have muscle and feel strong. And she wanted to find something she can do for the rest of her life," Alcantara said. "I totally understood where she was coming from."

Photo credit: Instagram / @kimkardashian