Kylie Jenner just revealed who her 'favorite sister' is -- and, no, it's not Kendall

OMG! Kylie Jenner just revealed who her favorite sister is, and it's not the one who you'd expect.

The 18-year-old social media maven grew up alongside her slightly-older sister Kendall, but on Monday, Kylie called another one of her famous siblings her "favorite sister."

SEE ALSO: Taylor Swift's new style will make you do a double-take

So, who's her favorite? Kourtney!

That's right, in a sweet birthday message that Kylie posted on Monday, she dropped the unexpected bombshell about her preferred sis.

"I love you Kourtney," she wrote in the caption of a hilarious face-swap video. "You already know you are my favorite sister these days."

Okay, to be fair, she did say "these days," but it's still a big admission! I mean, come on, how would you feel right now if you were Kim, Khloé or Kendall? Definitely a little bit jilted.

See photos of Kylie Jenner through the years:

"Thank you for teaching me to see the glass half full through everything," she continued. "Happy birthday <3"

Kylie made headlines this past weekend for her daring outfits at Coachella that included a Louis Vuitton bathing suit, rainbow braids and peach hair, to name just a few elements of her memorable ensembles.

Kourtney is currently in Iceland celebrating her birthday alongside her sister Kim, her husband Kanye West and a few friends, including Simon Huck and Jonathan Cheban.

See photos of Kylie Jenner's various Coachella looks:

More from AOL.com:
Samuel L. Jackson feuds with jilted fan: 'Stop whining!'
Mariah Carey dons sexy lingerie and heels while showing off her pizza-making skills
Rosie O'Donnell: Trump is like Harry Potter's Lord Voldemort