Kelly Clarkson tweets she's having a girl

Kelly Clarkson, who announced in November she and husband Brandon Blackstock were expecting, tweeted Monday that they are having a girl.

"We just found out we're having a girl officially!" the inaugural winner of "American Idol" wrote. "I knew it! Only a girl could cause this much drama with all this vomiting ha!" Clarkson, 31, already is stepmother to Blackstock's two children from a previous marriage. The singer and Blackstock were married Oct. 20.