World number two tennis player Serena Williams has become engaged to Alexis Ohanian, co-founder of the social media company Reddit.

"Down on 1 knee. He said four words. And/r/isaidyes," Williams said on the social media site on Thursday.

"I came home. A little late. Someone had a bag packed for me. And a carriage awaited. Destination: Rome ... back to where our stars first collided."

The New York-born Ohanian, 33, confirmed the news on his Facebook page, writing: "She said yes".