Paul Archuleta/Getty; Jerod Harris/Getty
On Thursday, Carter revealed that she is expecting her first baby with boyfriend Kristopher Brock by posting a photo of the couple on Instagram, which showed their shadows up against a rock wall and Carter's baby bump on full display.
In the comments section, Thompson - who is the mother of Carter's former husband Brody Jenner - wrote, "Yay! Now the news is out and I can tell everybody."
"I've been holding this in so long and I'm so excited for you! Congratulations! Can't wait to meet the little guy!" Thompson, 71, added, seemingly hinting at the sex of Carter's baby on the way.
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Kaitlynn carter/ instagram
Lindsey Carter Reis/ instagram
Later that same day, Carter's sister, Lindsey Carter Reis, shared a throwback post on her own Instagram, which was taken before the birth of her son Otto. Alongside the post she wrote that she's "so excited" for her sister.
In the comments section of the snapshot, Thompson first told Reis to "Enjoy these days… It's pretty much the best time of your life!"
"I didn't know The news about Kaitlynn being pregnant was out there yet so I've been very quiet about it…But I'm thrilled for her💜💜👏," she added.
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Carter and Brock have been dating since May 2020. The reality star was previously married to her The Hills co-star Jenner, 37, but the pair "decided to amicably separate" in August 2019, just one year after their Indonesian wedding. It was later revealed that their union was not legally binding.