The SKIMS mogul, 41, wished her former step-parent a happy 72nd birthday on her Instagram Story, posting a throwback photo of the two of them at the 2020 Vanity Fair Oscars party.
"Happy birthday @caitlynjenner," Kim wrote. "I love you so much and can't wait to celebrate you."
Her sister Kourtney Kardashian also shared some memories with Caitlyn, posting several photos from family outings in recent years. "Happy birthday!!" wrote Kourtney, 42.
One photo was from Caitlyn's 70th birthday dinner at Nobu Malibu in 2019. Kim and Kourtney were in attendance, as were Kendall, 25, Kylie, 24, Brody, 38, and Brandon Jenner, 40, as well as Brandon's now-wife Cayley Stoker and Caitlyn's friend and manager Sophia Hutchins.
Caitlyn welcomed Brody and Brandon with ex-wife Linda Thompson, 71, and she also shares daughter Cassandra Marino, 41, and son Burt Jenner, 43, with ex-wife Chrystie Scott. She was step-parent to Kourtney, Kim, Khloé, 37, and Rob Kardashian, 34, when she was married to Kris Jenner, 65, with whom she shares Kendall and Kylie.
Though Caitlyn came out as transgender in 2015, two years after she and Kris announced their separation, she told PEOPLE last year that some of her kids still call her "dad." "I'll be their dad until the day I die," Caitlyn said.
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The Olympic gold medalist is preparing to welcome two new grandchildren, as Kylie is expecting her second baby with Travis Scott, 30. Caitlyn spilled the beans just days before Kylie's official announcement in August, revealing that she had another grandkid on the way, and Kendall later revealed that Burt is expecting his third baby.
"Eighteen grandchildren. I keep telling the girls — they're not too excited about this, but — I wanna go for 30," Caitlyn said. "Thirty grandchildren. It's a round number. I just found out the other day that I have another one in the oven. Yes, I found that out the other day. So that's 19."