Serena Williams, one of the world's most successful tennis players of all time, has revealed in an Instagram post that she is an investor in cryptocurrency exchange Coinbase.

Williams took to the social media platform late last week to announce her VC firm Serena Ventures – which was secretly founded in 2014 – and listing some of its investments, including Coinbase and startups in areas such as fitness, clothing, food and women's health and community.

Williams said in the post:

The Serena Ventures website states that the company's portfolio includes over 30 firms with a total market capitalization of $12 billion. It is not clear how much was invested by her VC firm in Coinbase or in which round(s).

According to Crunchbase, Coinbase has seen investments totaling $546.6 million since its seed round in 2012. It most notably raised $300 million in a Series E round in October 2018, valuing the firm at $8 billion.

Forbes

indicates that, in 2018, Williams became the highest paid female athlete globally for the third year in a row, with earnings of around $18 million. She also has her own line of clothing and accessories.

As an athlete, Williams has achieved won a world record 23 Grand Slam singles titles in the Open era. She's also achieved 14 Grand Slam doubles titles alongside her sister Venus, and won four gold medals at the Olympics.

The Coinbase investment may not be such a surprise, as Williams' husband, Reddit founder Alexis Ohanian, was an early backer of the exchange through his venture capital firm, Initialized Capital.

Serena Williams image via Shutterstock; investments image via Serena Williams/Instagram