Tennis superstar Serena Williams will be a mother in four months time.

She announced today that she is five months pregnant in a photo of herself in a swimsuit showing off her baby bump.

“20 weeks,” she captioned the image on Snapchat Wednesday after posting a series of photos from a seemingly tropical getaway.

The implication of the good news is that the star was a few weeks pregnant when she beat her sister Venus to win the Australian Open back in January.

Fans were quick to praise the athlete for her superstar abilities and were mind-blown to learn she competed while a few weeks pregnant, the New York Daily News reported.

“Serena Williams won the Australian Open while she was pregnant. That woman is amazing,” one Twitter user wrote.

Another added, “Serena Williams was pregnant when she won the Australia Open in Jan. but I can’t even get out of bed when I’m on my period. Sis is superwoman.”

US Open organisers wished the star a big congratulations shortly after she revealed the news with a celebratory tweet.

“Serena Williams will have a new pride & joy to hug and call her own soon! Congratulations on the exciting baby announcement!” the post read.

Williams, 35, is engaged to Reddit co-founder Alexis Ohanian, 33. The US Open champion documented her whirlwind engagement on Reddit back in December with a poem.

Ohanian popped the question during an impromptu trip to Italy. He proposed at a restaurant in Rome at the same table where the duo first met on a lunch outing in 2015.

“This time he made it not by chance / But by choice / Down on one knee / He said 4 words And /isaidyes,” she wrote at the time, using the classic Reddit terms.

Williams and the techie began dating in October 2015 and didn’t discuss their relationship publicly until the engagement news bombshell.

On Monday, Williams shared an adorable snap of her fiancé holding her up in his arms on a beach. (NAN)

Update news