The tennis great gave birth to a baby girl - who she has named after her husband. but who exactly is her hubby-to-be Alexis, how long have they been dating and just how much is he worth?
Who is Alexis Ohanian?
Alexis Ohanian, 33, is a tech entrepreneur and best-selling author from the US.
He was born in Brooklyn, New York City, in 1983 to an Armenian-American father – whose family fled the genocide – and a German mother.
Alexis went to school in Ellicot City, Maryland, before graduating from the University of Virginia in 2005 with degrees in commerce and history.
He's most famous for co-founding social news website Reddit.
Along with business partner and fellow Virginia graduate Steve Huffman, the 6ft5 innovator set up the now-global name at the age of just 22.
The website went from strength to strength and was eventually snapped up by publishing giant Conde Nast – owners of Wired, GQ and Vogue magazines – the following year.
It was recently valued at £407million and is considered to be the seventh biggest site in the US.
Still a member of the site’s board of directors, Alexis was keen not to rest on his laurels.
He went on to launch social enterprise Breadpig in 2007 and helped set up travel search website Hipmunk in 2010, before co-founding the early stage venture capital firm Initialized Capital this year.
Alexis also wrote bestselling book Without Their Permission: How the 21st Century Will Be Made, Not Managed, which was published in 2013.
And he is a political activist – specifically in matters relating to the worldwide web.
He was dubbed “Mayor of the Internet” after his battles with US lawmakers over proposed bills aimed at cracking down on online copyright breaches.
When did Alexis Ohanian and Serena Williams get engaged?
Alexis and Serena got engaged in December last year. They had been dating - secretly - for 15 months after meeting in Rome.
The couple announced the news of their engagement on their social media accounts.
The lovers also posted a picture of them grinning from ear-to-ear and Serena showing off a spectacular rock in her diamond engagement ring.
In a poem posted on - where else? - Reddit, Serena 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.”
And Alexis shared the happy news on his Facebook page writing: “She said yes”.
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