The singer shared the happy news on Twitter on Monday: "We just found out we're having a girl officially! I knew it! Only a girl could cause this much drama with all this vomiting ha!"
Kelly, 31, had already predicted – and hoped – that she was pregnant with a little girl.
After confirming her pregnancy in November, she openly shared her thoughts. "I'm totally gonna have a girl. I'm manifesting it! And when I have a girl, you're gonna be like, 'That chick knew it!'" she joked.
Talking to Ellen DeGeneres, she did admit that they had bases covered when it came to names for a girl and for a boy. "Honestly, the name we've picked, if it's a boy or a girl, it's the same name," she told Ellen. "It's a random name. But it's not like … ‘Blue Jazz.' It’s not going to be a weird name."
Kelly tied the knot with talent manager Brandon Blackstock in October, and she made it no secret that she was hoping to be expecting a baby by Christmas.
In an interview with US radio show Valentine, the X singer said: "I want babies, yep I do!
"Everybody keeps saying, 'What do you want for Christmas?' And I'm like, 'I want to be pregnant.'"
And everything went exactly to plan, as just four weeks later the American Idol singer revealed she was, indeed, pregnant.
"I'm pregnant!!!," the delighted newlywed announced to her nine million followers on Twitter. "Brandon and I are so excited. Best early Christmas present ever."
Although it's Kelly's first pregnancy, she is no stranger to parenthood. The star is a step-mum to Brandon's children from his previous marriage, Seth, six, and Savannah, 12.
"My kids love her," Brandon's ex-wife Melissa told People in October. "I couldn't ask for a better stepmother for my children."