The snapshot shows Montag cradling her baby bump as she and Cavallari smile for the camera. Montag later posted the same photo on her own account.
"So much fun catching up with @kristincavallari," she wrote.
Montag announced in May that she's expecting a baby boy with husband and former The Hills co-star Spencer Pratt. She couldn't help but gush about Pratt while celebrating his 34th birthday Aug. 14.
"Happy birthday to the love of my life!" the star wrote. "You are the best husband and I know you will be the most amazing father!" "We are all so blessed to have you! Thank you for brightening up everyday of my life! I love you beyond words!"
Cavallari herself shares 5-year-old son Camden, 3-year-old son Jax and 21-month-old daughter Saylor with husband Jay Cutler.
She opened up about Saylor in an interview with People published Wednesday.
"We call her the honey badger because she's just pure sass," the star said. "She's adorable, but she will literally rip your face off."
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