The 35-year-old gave birth to a baby girl at a hospital in Palm Beach, Florida, on Friday, the source said.
The couple are yet to announce the name of the new bub.
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Serena accidentally announced her pregnancy back in April with a Snapchat selfie of her 20 week baby bump.
She's kept up her phenomenal level of fitness while expecting – winning the Australian Open at two months along while also continuing to share her kick arse pregnancy workouts on social media.
RELATED: Serena Williams Just Posted A Video Of Her Pregnancy Workouts
