"Our baby girl River Rose Blackstock arrived on June 12th!," the pop star tweeted Saturday. "Thank you everyone for all of your well wishes! Brandon and I are on cloud 9!! :)"
Clarkson, who during her pregnancy suffered horrible morning sickness, predicted way back in November that the little one would be a girl.
The "Catch My Breath" singer told Ellen DeGeneres in December that they'd already picked a "random" but not weird name for the child, one that worked whether they had a boy or a girl. We're guessing "Rose" was added after the gender ticket was finalized?
Clarkson, the first "American Idol" winnner and one of its most successful, married music manager Blackstock in a small Tennessee wedding in October after dating since late 2011. She'd tweeted word of their engagement on Dec. 15, 2012.
River is a first child for the singer. She's the third for music manager Blackstock -- happy Father's Day, dude! -- who also has a son and daughter from his first marriage to Melissa Ashworth.