Serena Williams has revealed she is 20 weeks pregnant.

The tennis legend took to Snapchat today to share a photo of her showing her tummy, titled '20 weeks'.

7 This was the photo Serena Williams shared on her Snapchat account, which she titled '20 weeks' Credit: Snapchat

The American sporting megastar is in a relationship with Reddit co-founder Alexis Ohanian.

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The 35-year-old is set to return as world number one next week - but this is set to be a short-lived reign with her set to miss the rest of the tennis season - including Wimbledon.

7 The happy couple shared this snap of them together on a beach yesterday, and now they have some special news to share Credit: Instagram

7 Alexis Ohanian is the co-founder of Reddit, meaning the pair are very much a 'power couple' Credit: Reddit

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That means she will be unable to defend her SW19 ladies' title - last year she saw of Angelique Kerber 7-5 6-3 to grab the silverware.

It also means that she was pregnant when she won Grand Slam title number 23 at the Australian Open in January this year.

Williams, who will return to world number one next week, would be eligible to retain her ranking under the WTA special ranking rule if she is ready to play her first tournament within 12 months of giving birth.

The photo was quickly deleted but her representative later confirmed the pregnancy.

And US Open Tennis responded: "Serena Williams will have a new pride and joy to hug and call her own soon! Congratulations on the exciting baby announcement!"

7 Alexis Ohanian has been dating Serena Williams now for almost 20 months, with the pair now engaged to be married Credit: Getty Images

7 Serena Williams surpassed Steffi Graf's number of Grand Slams this year when she won the Australian Open Credit: EPA

7 Serena Williams is regarded as one of tennis' greatest ever players Credit: Reuters

The couple announced they were engaged in December last year, after dating for 15 months.

And again the couple decided to share that news on social media too.

In the post titled ‘I said yes’, she wrote: “I came home / A little late / Someone had a bag packed for me

“And a carriage awaited / Destination: Rome

“To escort me to my very own “charming” / Back to where our stars first collided.

“And now it was full circle / At the same table we first met by chance

“This time he made it not by chance / But by choice

“Down on one knee / He said 4 words /And I said yes.”

Williams has not yet revealed a date for the big day, but The Sun has previously reported how Prince Harry could well be a guest due to his partner Meghan Markle being close friends with Serena.

Serena Williams' Grand Slam successes Serena Williams Wimbledon: 2002, 2003, 2009, 2010, 2012, 2015, 2016

US Open: 1999, 2002, 2008, 2012, 2013, 2014

French Open: 2002, 2013, 2015

Australian Open: 2003, 2005, 2007, 2009, 2010, 2015, 2017

7 Serena Williams and her fiance have not yet set a date for the wedding, but now have more pressing concerns Credit: MEGA

The 35-year-old collected her 23rd Grand Slam win of an amazing tennis career at this year’s Australian Open that saw her surpass the Open era record set by Steffi Graf.

She beat her sister Venus in the final 6-4, 6-4 to claim her seventh title at the Australian Open.

She has not played since that victory, citing a knee injury.

Other women have left the tour to have children and returned, including the Belgian player Kim Clijsters, who retired and had a child before coming back and winning three Grand Slam titles as a mother.

Williams, who has played professionally for two decades, first gained the No. 1 ranking in 2002 and has held that spot for more than six years in total during her career.

She is often regarded as the greatest female tennis player of all time.