In August, Clarkson announced her pregnancy during her concert at the Staples Center in Los Angeles, later admitting that the baby reveal "was not planned."
Clarkson posted a photo on Instagram of her first child, River Rose, smiling on a slide, and revealed her new baby's gender in the caption underneath.
"In other news, River's gonna have a little baby brother," Clarkson captioned the photo along with the hashtag #itsaboy. "We're so excited," she continued.
Clarkson and her husband Brandon Blackstock have been married since 2013, and have one other child, River Rose, together. Blackstock has two children from a previous marriage.