The official statement from Beyonce and Jay-Z came Monday afternoon.
"We are happy to announce the arrival of our beautiful daughter, Blue Ivy Carter," the couple said in a statement.
"Blue" is perhaps a nod to Jay-Z's "Blueprint" album franchise, and "IV" is the Roman numeral for the couple's favorite number, 4. They were both born on the 4th, married on the 4th and Beyonce's latest album was simply titled "4."
The couple said their baby was delivered naturally and weighed seven pounds. Jay-Z's song "Glory" gave fans the details of Blue Ivy's birth, calling her "the most beautiful girl in the world."
The song, posted on Life and Times, said it featured "B.I.C." - which would be the initials of Blue Ivy Carter. It reveals that Blue Ivy was conceived in Paris, and the song's refrain is: "The most amazing feeling I feel/Words can't describe what I'm feeling for real/ Maybe I paint the sky blue/My greatest creation was you. You. Glory."
Jay-Z also revealed in the song that Beyonce had a miscarriage at one point.
"Last time the miscarriage was so tragic/We was afraid you'd disappear/But nah baby you magic."
The sound of a baby's cries ends the song.
Celebs close to the couple have tweeted about the birth. Beyonce's sister, Solange Knowles, tweeted Sunday morning: "The most beautiful girl in the world," while Beyonce's close friend Gwyneth Paltrow also tweeted: "Welcome to the world Blue! We love you already."
It's the first child for the power couple who wed in 2008 in a private ceremony after a yearslong courtship.
Beyonce announced her pregnancy to the world last August at the MTV Video Music Awards with a simple rub of her swollen belly.
The couple gave birth at Lenox Hill Hospital in New York on Saturday. Hospital officials are shooting down reports that the couple paid over $1 million to rent a floor for the birth.
But one father of newborn twins says hospital security kept putting the hallway on lockdown, which prevented him and others from spending time with their babies.
"They should have gotten a little bit more strategic with where they put her. You can't cordon off the NICU. These are small children, newborns who need care, and you're just going to take over the hospital like you own it?" said Neil Nash-Coulon.
Hospital officials said while Beyonce and Jay-Z had their own security, they added that no security would have prevented a parent from gaining access to the neonatal intensive unit. Officials also said there were no official complaints made to hospital staff.
The Associated Press contributed to this report.