The 25-year-old "Heroes" alum and her fiance, Ukrainian boxer
"We are over the moon and madly in love!" the first-time parents told People in a statement.
Kaya Evdokia Klitschko -- as if the spelling of her parents' names weren't difficult enough -- weighed in at 7 pounds, 14 ounces, and measured 20 inches long, the mag said.
The heavyweight boxer, who towers over the petite actress, announced the news on Twitter in his native tongue.
"Nashville" wrote the pregnancy into the ABC drama's third season, making her country-star character with child too.
Panettiere and the Olympic gold medalist reportedly got engaged in March 2013, which is around the time she started wearing her gargantuan engagement ring.
The pair met in 2009 at an acquaintance's book launch and dated for two years before breaking up in 2011. Then they got back together in spring 2013, and she described their rekindled romance "like the 2.0 version."