The eldest and youngest siblings of the Kardashian/Jenner crew shared the news on Kourtney's 39th birthday.
"I am so excited to announce my collaboration with @kyliejenner 💋 We have been working on this for a year...3 mini eyeshadow palettes and 3 lips..I am wearing Matcha on my eyes and RAD on my lips. Happy Birthday to me!" the Keeping Up With The Kardashians star wrote.
Kylie also made the announcement on her Instagram account, along with a racy photo of the pair posing in nude swimwear and wearing one of the signature lipsticks from the KOURT X KYLIE collection.
Kylie has previously teamed up with Khloé and Kim Kardashian for her makeup line.
Will big sister Kendall Jenner be next?
KOURT X KYLIE will launch on April 24.