Tennis star Serena Williams has given birth to a baby girl at a clinic in Florida.
Williams, 35, whose partner is Reddit co-founder Alexis Ohanian, was admitted to the St Mary's Medical Center in West Palm Beach on Wednesday.
The 23-time Grand Slam winner said last month she was planning to return to tennis for the Australian Open in January.
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."
Five-time Grand Slam champion Venus has advanced to the fourth round at the open after beating Maria Sakkari of Greece 6-3 6-4.
The couple are yet to confirm the birth themselves but Serena's coach, Patrick Mouratoglou, tweeted: "I am so happy for you and I feel your emotion."
He added: "Btw ... I wish you a speedy recovery ... we have a lot of work ahead of us."
She won the Australian Open title this January while newly pregnant, and in an article in Vogue last month she said she wanted to defend her title.
"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."
In June she appeared in a nude cover photo for Vanity Fair, saying: "I don't know what to do with a baby."
The news has delighted the tennis world, with Rafa Nadal among the first to tweet his congratulations.
At a news conference, Garbine Muguruza who beat Venus Williams to claim the title at Wimbledon this year, joked; "a baby girl? Well, I hope she doesn't play tennis," Reuters reported.