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Sure, Christina Applegate is crazy in love with fiance Martyn LeNoble, but there's another li'l gal who's captured her heart even more: four-week-old daughter, Sadie Grace.

Her favorite part of being a mom? "Just being in love," the Hall Pass star, 39, told at the comedy's L.A. premiere Wednesday. "No offense to anyone that I know and love in my life, but you just really don't know love until you have that baby. You don't know. It's a whole 'nother ball game."

And while the actress says her and her rocker beau's baby girl isn't quite sleeping through the night yet -- "She's getting there," Applegate said -- she's already developing a personality.

"She's smiling and she's snarky," Applegate told Us. "She kind of looks at you and judges you."