The 30-year-old singer's wife Katy gave birth to their son Oliver Neil Allen on Tuesday, 30 July.
Kris confirmed the news via Twitter, writing: "Happy Day! My little stud was born today. Oliver is here people!"
The singer also shared an image of himself at the hospital dressed in scrubs, telling fans: "My outfit for the day. The best outfit I'll ever wear. #bestdayofmylife."
Kris didn't have the best start to the year after being injured in a head-on car collision on New Year's Day. His pregnant wife and dog were also in the car at the time. It was the accident that led him to announce his wife's pregnancy.
He tweeted at the time: "Thank you @ford for equipping me with a car that kept my whole family @katyallen @ZorroPup and the little one we have on the way safe."
"Yes I got in a really bad wreck tonight," he added, "and yes I'm having a lil baby. #gonnabeadaddy."
Kris won the eighth series of American Idol, which saw Adam Lambert finish in second place.
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