Image copyright Reddit/ AP Image caption The tennis star and the social media co-founder got engaged in Rome, where they first met.

Serena Williams has used the social media platform Reddit to announce that she is engaged to its co-founder, Alexis Ohanian.

The tennis star made the announcement in the form of a poem.

She said he took her to Rome, where they first met, to propose to her - and she said yes.

It caps off a year in which Ms Williams won her seventh Wimbledon singles title and 22nd Grand Slam singles title, but dropped to world number two ranking.

All you need to know about Serena Williams

Reddit is a social media community where users group around topics, news articles and discussion points, rather than around people they know in offline life.

Mr Ohanian founded it in 2005 alongside a college friend, Steve Huffman.

Ms Williams posted to r/isaidyes, a forum where users share their stories of wedding proposals, saying he had taken her to the table in Rome where they first met, where he got down on one knee and "said four words".

Image copyright Reddit

One Reddit user responded by joking that the score was love-love.

Mr Ohanian and Ms Williams had kept their relationship quiet on social media and in the world of celebrity gossip, but rumours began to circulate last year that they might be romantically linked.