"We have been blessed two times over", she said.
"They're here!" Knowles tweeted, along with the hashtags #beyonce #twins #jayz #happybirthday, but some of Beyoncé's fans responded that he should have waited to tweet until Bey herself had made her announcement.
Although they've only been breathing air for a few days, Beyoncé's twins have already enjoyed a long stay in the spotlight.
The Grammy victor singer revealed that she was pregnant with two back in early February with an Instagram post.
Beyoncé announced her pregnancy via Instagram on February 1.
The singer gave birth to the twins in a Los Angeles-area hospital some time last week, according to multiple sources.
Mali resort under attack by gunmen; at least 2 dead
State Department also warned U.S. citizens against traveling to Mali "because of ongoing terrorist attacks and criminal violence". Le Campement Kangaba resort in Dougourakoro, east of the capital, Bamako, is the site under attack, according to officials.
Jay Z helped to fuel the rumors when he failed to attend the Songwriters Hall of Fame Awards on Thursday night, although he was due to be honored.
Beyonce's father has apparently confirmed that the USA singer has welcomed her twins.
The gender and names of the twins have not been officially revealed.
But Beyonce recently showed off her large bump covered in an intricate henna design after her baby shower, which she spent with friends.
In the photo, which broke a record for the most liked picture on Instagram, Bey is surrounded by flowers and wearing a sheer veil over her head.
Beyonce also pulled the plug on plans to perform at the Coachella festival in California in April 2017 upon doctors' advice, and Lady Gaga stepped in for her.
Whilst Bey enjoys that precious first moments of her newborn children's lives, let's take a look back at her inspiration for that famous "Single Ladies" video.