FILE PHOTO - Tennis - Australian Open - Melbourne Park, Melbourne, Australia - early 29/1/17 Serena Williams of the U.S. poses with the Women's singles trophy after winning her final match. REUTERS/Thomas Peter/Files

LOS ANGELES (Reuters) - Tennis superstar Serena Williams is pregnant and expecting to deliver her first baby this fall, her spokeswoman said on Wednesday.

The confirmation, by publicist Kelly Bush Novak, came in a statement hours after the 35-year-old athlete posted a photo of herself in a yellow one-piece bathing suit on the social media site Snapchat with the caption "20 weeks."

Williams, who will return to the No. 1 ranking in the world next week, deleted the photo shortly after it appeared, and she waited more than six hours to make any public comment, stoking furious speculation about whether she was really expecting.

"I'm happy to confirm Serena is expecting a baby this fall," Los Angeles-based Bush Novak said.

If Williams is indeed 20 weeks into her term, that would mean she was approximately two months pregnant when she captured her record 23rd Grand Slam tournament title at the Australian Open in January.

Her victory over older sister Venus Williams broke a tie with Steffi Graf for the most Grand Slam singles championships in the sport's modern era. Serena Williams has not played since, citing a knee injury.

(Additional reporting by Frank Pingue and Steve Keating in Toronto, Jonathan Allen in New York; Editing by Grant McCool and Richard Chang)