Kylie Jenner shared a blast from the past on Thursday with an old-school family Christmas card that left several of her 399 million Instagram followers scratching their heads.

The 26-year-old cosmetics mogul — who recently freaked out her fans with a TikTok filter that made her look like Justin Bieber — posted a black-and-white family photo to her account that looked as if it was taken somewhere around the start of the Kardashian–Jenner clan’s first reality show, Keeping Up With The Kardashians.

But it was a second shot zooming in on the card’s text that most puzzled her fans and followers.

After a sweet message to their friends and family, the ‘Jenners and The Kardashians’ signed off with all of their names, except for unfamiliar name: ‘Casey.’

‘Who is Casey?’ wondered one fan in the comments.

Kylie Jenner, 26, shared a blast from the past on Thursday with an old-school family Christmas card that left several of her 399 million Instagram followers scratching their heads

A second shot of the card’s text confused fans, as it listed the entire family, as well as someone named ‘Casey’

Kylie also appeared to have cropped the photo at the top, leaving off that person on the end

‘Everyone wondering who Casey is and what did they do to her,’ summed up another user.

Another fan, seemingly noting that there was no one in the photo who could have been a ‘Casey,’ joked, ‘Is Casey in the room with us?’

The picture featured Kris Jenner and her spouse Caitlyn Jenner prior to her transition, along with Kris’ older children Kourtney, Kim, Khloé and Rob — formalized as Robert — Kardashian, along with Kris and Caitlyn’s younger daughter Kendall and Kylie Jenner.

The mysterious ‘Casey’ referred to a missing half-sibling, Caitlyn’s daughter Cassandra Marino, who sometimes goes by the diminutive nickname.

The Olympic gold medalist shares her daughter, now 43, with her first wife Chrystie Scott, whom she was married to from 1972 to 1981.

The couple also share an older son, Burt Jenner, 45, whose name wasn’t even included on the photo.

Days after her first divorce was finalized, Caitlyn married Linda Thompson, with whom she went on to welcome two sons: Brandon and Brody Jenner, both of whom were also absent in name and photo from the Christmas card.

Cassandra’s ghostly presence on the card, as well as the complete absence of her other children from her prior marriages, may be related to her reported estrangement from many of her children.

But fans wondering who ‘Casey’ was didn’t realize that she is Caitlyn Jenner’s daughter Cassandra Marino, from her first marriage to Chrystie Scott; (L–R) Cassandra seen with Caitlyn, Brody Jenner, Linda Thompson and Brandon Jenner; seen in 2019

The couple also share an older son, Burt Jenner (L), 45, whose name wasn’t even included on the photo

It’s not clear if Kylie cut out ‘Casey’ to protect her privacy, as she has kept a lower profile over the years than her siblings, or due to some animosity. But Caitlyn’s children from her first two marriages all declined to participate in her reality show years earlier

In 2019, Brody Jenner recalled seeing little of Caitlyn when he was a child after she married her third wife Kris Jenner, and he later vowed to do the ‘exact opposite’ by being the ‘absolute best father’ to his first child, whom he welcomed in July with fiancée Tia Blanco; seen in 2016

In a 2015 interview for CBS’ This Morning, Buzz Bissinger, the journalist who wrote Caitlyn Jenner’s Vanity Fair cover story that year announcing her name change amid her gender transition, shared that her older children had declined to participate in her reality series I Am Cait.

‘That was a hard decision for them, because these are Jenner kids, trying to reconnect with their father after a long, long absence,’ Bissinger said, via Page Six.

Cassandra, an interior designer, has kept an even lower profile than the rest of her siblings.

Several fans who figured out who ‘Casey’ referred to wondered in the comments why Kris and Caitlyn and included her — despite Cassandra not appearing in the family photo — while not even mention Burt, Brandon or Brody.

However, some eagle-eyed fans noticed that the picture Kylie posted appeared to be cropped, and the second image of the text showed the bottom of the photo while hinting at the silhouette of an additional person to the right of Rob, which may have been Cassandra.

It’s unclear if Kylie cropped the figure out to protect her half-sister’s privacy or due to family conflict.

‘Why they put bruce daughter n not his sons then,’ pondered one user in the comments.

‘I’d be insulted if my name was there but not my photo,’ joked another fan.

During a 2019 episode of The Hills: New Beginnings, Brody Jenner confessed that he ‘didn’t really grow up’ with Caitlyn as a stable parenting figure.

While Kylie was posting family throwbacks, her boyfriend Timothée Chalamet, 27, kept a low profile as he shopped at a Chanel boutique in Beverly Hills on Friday

The Wonka actor donned a Celine hoodie with a baseball cap underneath, as well as oversized pants and green sneakers

‘When I was really little, we got to spend a little bit of time. But when [she] started the family with the Kardashian family and all that, I didn’t really see much of [her],’ he continued.

In August, he mused on how he planned to approach parenthood with his fiancée Tia Blanco after they welcomed their first child in July.

‘[Caitlyn] wasn’t really around for me growing up,’ he shared in a YouTube clip.

The reality star said he planned to do the ‘exact opposite’ of Caitlyn, by ‘being the absolute best father I could possibly be and getting ready for the journey and just so very excited.’

While Kylie was posting family throwbacks, her boyfriend Timothée Chalamet, 27, kept a low profile as he shopped at a Chanel boutique in Beverly Hills on Friday.

The Wonka actor donned a Celine hoodie with a baseball cap underneath, as well as oversized pants and green sneakers.

Kylie and Timothee have been linked since April.