The Grammy Award-winning artist is said to be in her first trimester of pregnancy, which reportedly came as something of a surprise.
"B was shocked. She loves kids, but she wasn't ready to be a mother just yet," said a source close to the singer. "She really wanted to get her album done and tour the world again."
Another insider said Beyonce, 29, believed "this is a gift from God, and she's so happy."
The couple have not yet confirmed the news -- and Beyonce has been subject to false pregnancy rumors in the past, notably in March when U.S. website Mediatakeout reported Jay-Z was "extremely happy to be having his first child with Bey."
Regardless of this, Wednesday's report quickly took Twitter by storm.
"Please let little Jay Z and Beyonce look JUST like the Mommy," one fan wrote, as another added, "Shout out to jay and Beyonce on they 1st child."
Celebrities were also starting to pass on congratulations to the couple.
"Jay has been all about family since I met him, and he's always going to be," record executive Kevin Liles, a longtime friend of the couple, told Us Weekly. "I wish them the best."
Beyonce married Jay-Z, 40, in a low-key ceremony in 2008.
They are notoriously private about their relationship, but Beyonce made no secret of her desire to have kids in the past.
"I definitely want to have a child, but I know from my nephew it's a lot. I hope that those things will just happen naturally. I still haven't had time to relax," she told Allure magazine earlier this year.
Beyonce's nephew is Daniel, the son of her sister Solange Knowles, who said Beyonce would make a "great mom."
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