Sizzling siblings!

Kylie Jenner and Kourtney Kardashian stripped down to nude bathing suits to announce their KOURT X KYLIE makeup collaboration, and they certainly know the tricks of the trade for self-promotion.

The cosmetics collab comes complete with three eyeshadows and three lip kits, and it's bound to sell out quickly!

"HAPPY BIRTHDAY TO THE QUEEN! 👑 so excited to announce the KOURT X KYLIE collaboration. This collection gives me so much lifeeeee! 3 mini palettes & 3 of Kourtney's signature lippies launching 4/24! collaborating with you was so much fun! I love you!" Kylie captioned an Instagram post of the announcement.

It still blows our mind that Kyls has built a billion dollar brand in just a few years!