'Who's Casey?': Kylie Jenner Confuses Fans With Throwback Christmas Card Featuring Unknown Family Member

Kylie Jenner left fans puzzled when she posted her "favorite" family Christmas card on Instagram.

The black and white throwback snap shared on Thursday, December 21, featured all of her siblings — Kendall Jenner and Kourtney, Khloé, Kim and Rob Kardashian — as well as her parents, Kris and Caitlyn Jenner.

"Life is not measured by how many breaths we take, but by the moments that take our breath away," the card read. "May you be blessed with many breath-taking moments."

"Merry Christmas, With Love, The Jenners and The Kardashians. Bruce, Kris, Kourtney, Casey, Kimberly, Khloé, Robert, Kendall & Kylie," the message concluded, which was written before Caitlyn transitioned from Bruce Jenner.

Fans were confused since Casey — the lesser known daughter of Caitlyn and her ex-wife Chrystie Scott — wasn't in the picture, and she hasn't been mentioned much, if at all, on the family's shows.

Since the Kylie Cosmetics founder, 26, didn't clarify who her half-sibling was on the upload, the comments section was flooded with questions.

"Everyone wondering who Casey is and what did they do to her," one Instagram user quipped, while another asked, "Is Casey in the room with us?"

"Did Casey take the pic," questioned another fan, while a fourth penned, "So are we all here asking the same question? Who is Casey? 😩."

Meanwhile, big sister Khloé, 39, loved the old shot, commenting, "❤️❤️❤️❤️❤️," while Kourtney gave it a "like."

As OK! reported, Caitlyn's relationship with Kendall and Kylie soured a bit after the I Am Cait star, 74, discussed the family dynamic on a U.K. talk show in October.

"Well Kris, I really never talk to anymore. Yeah, it's sad," the Olympian spilled. "If there's any communication, my manager kind of talks to her, and when you have as many kids as I have, you're closer to some than you are to others … I certainly see them and we do this and that. I'm much closer to the Jenner side, but Kris, I don't really have any more contact with her. It's kind of sad because we went through a lot."

She also stated on House of Kardashian that Kim, 43, was "calculated" when it came to becoming famous.

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