Williams announced her pregnancy with Reddit co-founder Alexis Olhanian in April by posting a selfie on Snapchat with the caption “20 weeks”.
The US Open was among the first to tweet the news.
Reports claimed that an entire floor of the St Mary’s Medical Centre had been cleared to offer Williams maximum privacy.
“Obviously I’m super excited,” said the baby’s aunt, Venus Williams, as she took the court at the US Open. “Words can’t describe.”
Citing a source from St Mary’s Medical Centre in West Palm Beach, where Williams reportedly checked in on Wednesday to be induced, WPBF editor Patricia Storm said the new addition weighed in at 3.09 kilograms and was delivered via Caesarean section. Both mother and baby are said to be healthy.
Congratulations to @serenawilliams for giving birth to a baby girl!
— US Open Tennis (@usopen) September 1, 2017