Casey and Kylie Jenner are certainly familiar with each other – even if the internet has no idea who the former is. Photo: @KardashianBish/Twitter

• Kylie set Instagram alight this Christmas when she posted a holiday photo with an inscription mentioning family members Kris, Kourtney, Kim, Khloé, and Kendall – and a ‘mysterious’ Casey
• As one of Caitlyn Jenner’s lesser-known children, Casey has shied away from the spotlight – unlike her famous siblings – and, no, she wasn’t in I Am Cait either
• 

Kylie Jenner recently set off a social media detective hunt when she posted a throwback photo of her family at Christmas – with one “mystery” name signing off the card along with the famous clan.

Fan comments reveal confusion about the text beneath the photo Kylie Jenner posted recently. Photo: @kyliejenner/Instagram

The photo inscription read, “Merry Christmas, with love, The Jenners and The Kardashians, Bruce, Kris, Kourtney, Casey, Kimberly, Khloé, Robert, Kendall and Kylie.”

Kylie Jenner posted this at Christmas and confused plenty of people in the process. Photo: @kyliejenner/Instagram

Netizens quickly took to the comments section to express their confusion as one name stood out on the list – Casey – although she doesn’t appear in the photograph.

“Everyone wondering who Casey is and what did they do to her,” wrote one commenter.

Cassandra Marino, Caitlyn Jenner, Brody Jenner, Linda Thompson and Brandon Jenner pictured together in May 2019 in Malibu, California. Photo: Getty ImagesBut the search didn’t last too long as internet sleuths were quick to decipher the identity of the seemingly unknown Kardashian-Jenner.

Casey, full name Cassandra “Casey” Marino, is in fact one of Caitlyn Jenner’s children from her marriage to now ex-wife Chrystie Scott, according to US media. That makes Casey Kendall and Kylie Jenner’s half-sister.

Here’s what we know about the lesser known Jenner.

How is Casey Jenner related to the Kardashians?

Clockwise from top left: Burton Jenner, Khloe Kardashian, Bruce Jenner, Kris Jenner, Kim Kardashian, Brandon Jenner, Brody Jenner, Kourtney Kardashian, Robert Kardashian, Jr. and Cassandra Jenner pose for a family portrait in 1993. Photo: Getty

Cassandra Marino, aka Casey, is the second child of Caitlyn Jenner and her first wife Chrystie Scott. Per Vanity Fair, Casey, 43, was born in the midst of her parents’ divorce, and Jenner was reportedly not present at the time of her birth.

Jenner was then married to Linda Thompson, Elvis Presley’s ex-girlfriend, until 1986, and then Kris Jenner, whom she divorced in 2015. Jenner’s oldest child with Chrystie Scott is 45-year-old Burt Jenner, Casey’s brother, and she also shares two sons – Brandon, 42, and Brody, 40 – with Linda Thompson. Jenner’s youngest children are of course Kendall, 28, and Kylie, 26.

Casey Jenner is an interior designer

Cassandra Marino and RHOBH star Taylor Armstrong at a Fendi event in Beverly Hills in 2011. Photo: Getty Images

According to People, Casey works as an interior designer. There aren’t many more details about her work though, which isn’t too surprising because she remains largely away from the spotlight and social media – let alone reality TV.

She’s married with children

Casey Jenner and her two daughters Isabella and Francesca. Photo: @KKRKKJ/Twitter

It’s no secret that the Kardashian-Jenner clan is an ever expanding one, and that extends beyond its most famous members Kim, Kourtney and Khloé, who all have children of their own too.

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According to Sportskeeda, Casey is married to a man called Michael Marino and has three children: daughters Francesca and Isabella and a son, Luke.

She’s had her ups and downs with Caitlyn Jenner

As Casey has revealed in one or two rare interviews, it’s not all been smooth sailing for her and Caitlyn Jenner.

According to Vanity Fair, the first time Cassandra met Caitlyn, it was during one of Jenner’s “girls’ nights” – hangouts where Caitlyn began hosting as part of her transition, “where [Caitlyn] could dress as desired and feel natural in the presence of women.” Per Sportskeeda, Casey has known about Caitlyn’s transition since she was 11 years old.

“My relationship with Caitlyn is much better than with Bruce, but we still have a lot of work to do,” she told People. “We didn’t talk for years, and now we see each other every couple of weeks and talk on the phone, which I am grateful for.”

(L-R) David Foster, guest, Burt Jenner, Caitlyn Jenner, Leah Jenner, Brandon Jenner, Eva James Jenner, Linda Thompson, Brody Jenner, Aaron Foster, Michael Marino, Cassandra Marino and Chrystie Scott in 2016. Photo: Getty Images

However, in 2015, according to Sportskeeda, Casey, her brother Burt and half-brothers Brandon and Brody chose not to partake in their parent’s docuseries I Am Cait, following her transition.

As reported by People, it seems like they’re still on good terms as Caitlyn joined her eldest daughter and her family to celebrate Thanksgiving and Christmas together in 2021.

“Great thanksgiving. Great meal. Thank you to my daughter Casey for opening her home,” the transgender icon captioned a pic for the holidays.