LOS ANGELES (AFP, Reuters) - Tennis superstar Serena Williams is pregnant and expecting to deliver her first baby this fall, her spokeswoman said on Wednesday (April 19).

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.

Novak told Reuters that Williams "definitely" would not be able to play again this year but "looks forward to returning in 2018".

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.

For fans the announcement underscored Williams' superwoman status.

"Serena Williams was pregnant when she won her 23rd grand slam tournament at the Australian Open. And did not drop ONE SET. Let that sink in," Twitter user @noelleharmony posted.

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.

In December, Williams announced her engagement to Reddit co-founder Alexis Ohanian, first sharing that news on the Reddit social media site.