Addressing her 130 million followers, the 21-year-old reality maven captioned the shot:
"Back at it again with nail bae."
Kylie shares one-year-old daughter Stormi Webster with her rapper beau Travis Scott.
Heather - Jenner's closest confidante since her longtime "wifey" Jordyn Woods hooked up with Khloe Kardashian's boyfriend Tristan Thompson - is also a young mother to two children.
The Sorella Boutique founder was pregnant with her youngest, Zane, at the same time Kylie was expecting Stormi.
Fans went into a frenzy over the post, with one declaring: "You heard it here first. I think Kylie Jenner is pregnant again."
"Back at it again with nail bae - more like back at it again with a second baby," another tweeted.
It's not the first time the youngest of the Kardashian-Jenner clan has prompted whispers of a second baby.
On February 3, the Kylie Cosmetics creator posted a sweet snap of her and Scott locked in an embrace on the staircase of her Calabasas mansion with the caption: "baby #2?"
Kylie also reportedly bowed out from much of the filming for season 16 of Keeping Up With the Kardashians after news of Tristan and Jordyn's cheating emerged.
A source told Us Weekly: "Kylie took a little break from filming Keeping Up With The Kardashians and recently got back into filming and it’s been a struggle and difficult.
"She was very upset about the situation with Jordyn and also just didn’t want to deal with it and have to address it."
Her almost total absence from the newly released KUWTK trailer prompted fans to speculate that she was lying low because she is expecting again.
Watch the trailer here!