The singer, 32, announced the couple’s happy news on Twitter on Saturday, June 14:
Clarkson, who married Reba McEntire’s stepson in Tennessee last October, revealed that she wanted children right away and predicted that she would have a girl first.
When her prediction turned out to be true three months later, she tweeted, “I knew it! Only a girl could cause this much drama with all this vomiting ha!”
Blackstock has two children from a previous relationship, 12-year-old daughter Savannah, and 8-year-old son Seth.
We can’t wait to see a pic of baby River Rose!