Tennis player Serena Williams has revealed on social media that she and Alexis Ohanian, the co-founder of Reddit are engaged.

A spokesperson for Ohanian said that he asked Williams to marry him while they were on holiday in Rome. Williams, current number two player in the world, revealed the news in a Reddit post on its "r/isaidyes" forum, where users share stories of wedding proposals.

The 35-year-old said the entrepreneur had taken her to the table in Rome where they first met, where he got down on one knee and "said four words".

Ohanian made public the engagement on his Facebook page, according to CNN, with a link to Williams' Reddit post, writing: "She said yes."

The couple are believed to have been dating since 2015, and have tried to keep their relationship out of the media's spotlight.

However, US Weekly broke the news that they were romantically involved in October 2015. A source told the newspaper that "he'd never been into tennis until they started dating!"

Williams and Ohanian were first seen together having dinner at Mission Chinese in San Francisco in November 2015, when surveillance video released by the restaurant came to light.

It was during that date, a man stole the tennis player's mobile phone from the table and quickly left the restaurant. Williams chased down the phone thief, saying it was the "craziest thing" that has ever happened to her.

A wedding date has not yet been disclosed. Williams, who won the Wimbledon Championships this year, is preparing for the Australian Open next month. The US tennis player has previously dated Drake, Common and Grigor Dimitrov.

Williams' net wealth is believed to be around $150m in 2016, according to Forbes. She is number 40 on the list of world's highest-paid athletes.

Her future husband has a net worth of about $4m, according to The Heavy. Ohanian founded Reddit, a social media community in 2005 alongside a college friend, Steve Huffman.

The World Tennis Association (WTA) tweeted congratulations.