Serena Williams and Reddit co-founder Alexis Ohanian are engaged.

American professional tennis player, Serena Williams has announced her engagement to the co-founder of Reddit, Alexis Ohanian.

Williams surprised the world by announcing the engagement in a poem on a Reddit thread for people to share their engagement stories "r/isaidyes" forum.

According to the poem posted from her verified Reddit account, Ohanian proposed at the place they first met during a surprise trip to Rome.

"I came home/A little late/Someone had a bag packed for me/And a carriage awaited" Williams said in her Reddit post, which was written like a poem and had a cartoon of the couple at the top.

Serena Williams engaged to Reddit co-founder Alexis Ohanian (Google)

"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/r/isaidyes."

Ohanian also announced the engagement on his Facebook page, linking to Williams' Reddit post and adding, "She said yes."

He also commented on her Reddit thread, writing,  “and you made me the happiest man on the planet”.

Apparently, the couple have been dating since late 2015, but have been keeping it low key except for a few Instagram posts.