EXCLUSIVE: Kristin Cavallari Gushes Over Lauren Conrad's Pregnancy Announcement: 'I'm So Happy For Her'

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It feels like a million years ago since Kristin Cavallari and L.C. catfought over Stephen Colletti in Cabo...

Especially now that Lauren Conrad has announced she is expecting her first child with husband William Tell. ET caught up with Cavallari, Conrad's former Laguna Beach and The Hills co-star, at Sunday night's NBCUniversal Golden Globes after-party and the mother of three could not have been more thrilled for her former frenemy.

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"I haven't talked to her in years, but what an exciting time in her life!" she told ET's Leanne Aguilera. "I'm so happy for her, and it's cool to see the evolution of everybody from The Hills and Laguna Beach and to see how everyone is growing up. It's been really fun to watch!"

Cavallari recently celebrated a life milestone of her own: the former reality star turned 30 on Jan. 5, and revealed on Instagram that husband Jay Cutler "really went all out" to make her big day special.

"My husband threw me a huge surprise party. I was completely surprised," she exclaimed. "And we're actually going to Mexico this coming weekend, so my birthday continues! I'm excited."

WATCH: Kristin Cavallari Shares Tribute to Late Brother One Year After His Death

Don't expect her birthday shenanigans to get too wild, though, as Cavallari revealed that being a mom to three kids under the age of five -- Camden, 4, Jaxon, 2, and Saylor, 1 -- has hampered her ability to party.

"I'll probably have one drink and go home and go to bed. I've become such an old lady," she said of her Globe party plans. "I gotta go be a mom tomorrow. I can't be hungover at all. I can't do it like I used to!"

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