As Life & Style reported last week, Kourtney Kardashian is pregnant with her fourth child — and the 37-year-old recently showed off her mini baby bump in a bikini pic on Instagram!

"On a Saturday," the brunette beauty captioned the photo, which shows her on the side of a cliff.

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On a Saturday. 🇺🇸

A post shared by Kourtney Kardashian (@kourtneykardash) on

The identity of her baby's daddy still remains a mystery, with a source telling Life & Style, “At first, everyone just assumed it was Scott [Disick's] since he’s been trying to make things work, but then out of the blue, she jets off to spend time with Justin [Bieber]. Her close friends and even her sisters aren't sure anymore."

RELATED: Scott Disick Posts Shockingly Intimate Photo of Kourtney Kardashian!

The source added, "A paternity test is the only answer at this point, but it’s the last thing in the world she wants to do. This whole thing has her stressed out like you wouldn’t believe!”

For a look back at Kourtney's best maternity style, scroll through the gallery below!