Kristin Cavallari Is About to Pop -- Wait Until You See Her Big Baby Bump Now!

The "Hills" star showed off her big baby bump on Instagram on Thursday in a photo taken by her son, Camden, 2.

In the pic, the mama-to-be flashes her belly underneath her "Preggers" T-shirt as she stands in the kitchen with a coffee cup in hand. "Even my preggers shirt is too small," she jokes before giving her little one credit for the sweet snapshot. "#HeBetterNotStartChargingMe #ReadyWheneverYouAreBaby."

The mother-of-three is excited to welcome a little girl into the household. She recently revealed that her daughter will steal daddy Jay's Cutler's heart and also be good for her boys, Cam, and Jaxon, 17 months.

"I'm excited for the boys to grow up with a sister," she told American Baby earlier this month. "I think it will help them to better understand and respect women."

The proud mama couldn't help but gush about her sons, admitting that her boys are opposites. "Camden was such an easy baby. Jaxon is more of our rebel wild child, but he's also a mama's boy," she said. "Our little girl will have her own personality. I know I can't change who they are. It's important to let kids be themselves and to let them make mistakes. Self-discovery goes a long way."

The 28-year-old star said she realizes what she's getting into the third time around. "Having an infant is stressful, and I know I won't get a lot of sleep initially, but it will be worth it,” she admitted. “Jay and I want our kids to be close in age, so they can have a tight bond. And we'll get the diaper phase out of the way!"