The news was reported by Roger Friedman's entertainment portal ShowBiz 411, reports variety.com.
It is unknown precisely when the singer gave birth, though it stands to reason that it would have been on or around June 15, as Jay Z was due to be honoured that night in New York City at the Songwriters Hall of Fame, but did not attend the ceremony.
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The sex of the twins is also unknown, but former US President Barack Obama hinted at the arrival of two girls in a video message broadcast at the Songwriters Hall of Fame. They will join big sister Blue Ivy Carter, born in January 2012.
"Bey and Jay are thrilled and have started sharing the news with their family and closest friends," people.com quoted a source as saying.
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Beyoncé announced her pregnancy via Instagram on February 1. Beyoncé has kept a low profile in recent months, dropping out of Coachella (she was replaced by Lady Gaga) in April and skipping the Met Gala in May.
Representatives for the couple have not responded to requests for comment, variety.com said.