Tennis star Serena Williams confirms pregnancy

Tennis superstar Serena Williams is pregnant and is due in autumn, her spokeswoman has confirmed.

The official confirmation comes just hours after the 35-year-old athlete posted a photo of herself in a yellow bathing suit on social media site Snapchat with the caption "20 weeks."

The image shared by the 23-time grand slam singles champion shows her to have a small but noticeable bump.

Serena Williams shared this image with fans. Credit: Snapchat/Serena Williams

Williams, who won the Australian Open in January, announced her engagement to Reddit co-founder Alexis Ohanian in December.

She posted a loved-up picture of herself in her fiance's arms on Instagram two days ago with the caption "My only regret is not pointing my toe sorry coach Garry".

The tennis star's spokeswoman said Serena "definitely" would not be able to play again this year but "looks forward to returning in 2018".

Fans have been rushing to congratulate her on the news - and pointing out that the post suggests that she was already pregnant when she won the Australian Open.