"I thought I'd be the last," Cavallari – whose hard-partying antics were captured on Laguna Beach and The Hills – told PEOPLE with a laugh on Wednesday, when asked about getting pregnant before any of her former costars. "I had thought it was so far from where we were, so it's not really something that [I considered then]."
In fact, it was her so-called nemesis Lauren Conrad whom Cavallari, 27, expected to settle down before anyone else.
"Lauren always seemed like she wanted to get married and have kids, so I wouldn't have been surprised if she was maybe the first one," Cavallari says.
But with baby no. 2 on the way in May, E!'s The Fabulist co-host says her domesticated life could not feel more natural and fitting.
"Everything just fell into place and it all worked out," she explains. "It's funny that I am the first, but it feels so right, so it's perfect."
Although Cavallari is the first Hills alum to have a baby – son Camden Jack is now 19 months old – it seems her fellow former cast mates could be catching up soon enough.
Conrad's ex-boyfriend and former costar Jason Wahler married Ashley Slack in October, while Conrad and Whitney Port both recently announced their engagements. And reality TV's formerly most hated couple Heidi Montag and Spencer Pratt will celebrate their five-year wedding anniversary in April, managing to outlast many other Hollywood couples.
"I don't talk to Jason anymore, but I saw a picture [from his wedding], and I'm happy for him," Cavallari said. "I don't talk to Lauren, and I've seen Whitney maybe two times since we've stopped filming. Unfortunately I don't talk to them, but I'm so happy for them. It's such an exciting time in their lives. It's fun, you know? Planning a wedding is overwhelming, but it's such a blast."
Cavallari, who hasn't gotten morning sickness during either of her pregnancies, says she's feeling "really good." Her joy is evident on the upcoming cover of Fit Pregnancy (see it first on PEOPLE.com Friday!), in which the glowing starlet poses with a smile, holding her baby bump and showing off her fit physique.
"I'm happy with it," she said. "I feel like they did a really good job with the florals for spring. I think the cover is really fresh and clean and I'm really excited about it."
And although her cover could be considered conservative compared to more risqué pregnancy shoots in the past, the Chicago resident wouldn't have hers any other way.
"To be honest, I don't think [posing pregnant and naked] is something that a lot of people necessarily want to see," she said. "My personal preference is it's something to be kept for my husband and I, but hey, if you want to do it and you feel confident, then all power to you."