Mum-of-three Kourtney was first to share her sexy snap on social media.
Flaunting her oiled up bare belly and a lot of cleavage which was just about covered up by her hair, the reality beauty looks as hot as ever.
The star was also sporting a hint of baby bump and captioned the snap: “TBT pregnant mermaid.”
Judging by her belly button ring, Kourtney must have been pregnant with Mason who is now six.
Khloe also shared pictures of her own as she poses topless save for a black mermaid-style skirt.
"These pictures have never seen the light of day!" she wrote.
"There were a couple of cute behind-the-scenes images, though."