Entertainment Tonight reported Montag wore a bikini from her "The Hills" co-star Audrina Patridge's swimwear line, Prey Swim, in the snapshot. The star was seven months pregnant at the time of the photo.
Montag announced her pregnancy in April, and confirmed the next month that she and Pratt are expecting a baby boy.
She said in an interview with Us Weekly that it was "in [her] heart" to have a son.
"I thought Spencer really used to want a boy, and then a few months ago we had a conversation where he said, 'Let's just make sure it's healthy. Boy or girl, I don't care,'" the star recalled.
"I hope to have a little girl one day, but for my first child, I really wanted a son," she shared. "I thought it'd be a more natural bond for Spencer since he and his dad are so close."
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