Serena Williams gave birth on Friday at the St Mary’s Medical Center in West Palm Beach, prompting congratulatory messages to begin circulating on social media.
The news was first broken by a TV news producer Chris Shepherd on Twitter.
“Tennis star Serena Williams gives birth to a baby girl weighing 6 pounds, 13 ounces. Mom and baby doing well,” he wrote.
News of the birth came as her sister Venus prepared to go out on court at the US Open.
“Obviously I’m super-excited,” Venus said. “Words can’t describe it.”
Serena had admitted to be pregnant to the world in April by accident, after mistakenly uploading a photograph on Snapchat.
She had won the Australian Open title this January while newly pregnant, “It’s the most outrageous plan,” she said. “I just want to put that out there. That’s, like, three months after I give birth.”
Williams who has a slew of records to her name, including as the only tennis player to have won 10 Grand Slam singles titles in two separate decades. She is also the only player to have won two of the four Grand Slams – Wimbeldon and the Australian Open – seven times each.
In an earlier Vogue interview, the 35-year-old had revealed that she “definitely” plans to return to the court.
Williams, 35, whose partner is Reddit co-founder Alexis Ohanian, said last month she was planning to return to tennis for the Australian Open in January.
“It’s hard to figure out what the end of your tennis career should look like,” she says. “I used to think I’d want to retire when I have kids, but no. I’m definitely coming back. Walking out there and hearing the crowd, it may seem like nothing. But there’s no better feeling in the world.”