Kylie Jenner Makes Her Music Debut in 'Fourth Strike' With Terror Jr

Kylie Jenner is proving she's the baddest b*tch around ... 'cause she just made her musical debut -- using her King Kylie alter ego!

That's right -- King Kylie is back ... and collabed with Los Angeles duo Terror Jr for a sexy new single, "Fourth Strike."

Kylie shared the breathy song on her official YouTube page and fans can hear her sultry yet crisp vocals toward the end of the song as she croons ... "One strike, two strike, let me get the mood right ... Do it on purpose just to see how it ends." She closes out her verse by whispering "King Kylie."

As fans know, the makeup mogul is using the song to promote her new nostalgic Kylie Cosmetics makeup launch featuring her colorful It-Girl King Kylie aesthetic from the mid 2010s.

It's featured in a new promotional video -- dubbed "Glosses Part 2" -- that picked up where her viral promo clip from 2016 left off -- her in police custody for being too good at being, well ... bad.

"Fourth Strike" is quite the iconic way to promote her new launch, considering she was rumored to be the vocalist behind Terror Jr's "Three Strikes" when it came out in 2016 ... though she denied the rumors at the time.

Kylie celebrated the song's release and mentioned the OG rumors in an Instagram post she share midnight Tuesday, gushing she was "soooooo nervous but so grateful" that Terror Jr trusted her to collab on the song.