Singer Christina Perri is a new mum after welcoming a baby daughter.

The A Thousand Years star's new husband Paul Costabile has posted a photo of the family on Instagram, calling his baby daughter "the greatest gift we've ever known".

"Welcome to the world Carmella Stanley Costabile...," he adds. "Mom and our little principessa are doing great. Dad can't stop crying!"

The couple had no idea about the sex of the baby until little Carmella was born.

Paul previously said, "In a world of so much technology, we kind of decided to just wait and see what happens because we'd rather be surprised the day of. It's been an exciting waiting time."

Perri and Costabile tied the knot last month (Dec17) on the fourth anniversary of the day they first met.

The singer shared a romantic photo of the newlyweds on Instagram on 12 December (17), adding the caption: "On this day four years ago, we met. today, WE GOT MARRIED!!!"

Paul also gushed about their union on the picture sharing site, adding: "4 years ago today I met my dream girl in this room (sic). 4 years later today I married my dream girl and best friend. Pretty sure I’m the proudest I’ve EVER been to be able to call the most bellissima person + woman I’ve ever known now my wife!!! Whoa.

"I thank God for the gift of her, our relationship, our bambino on the way, our family’s love and support and this unforgettable year. And for friends and fam (family) wondering... invites to an official shindig coming soon... now I’m going to go scream this news on rooftops across this town because I AM that guy."

The couple became engaged in June (17), when TV personality Costabile opened up about falling for his new fiancee before an interview.

Perri announced she was pregnant in August (17).