Serena Williams is set to retire from tennis in the coming weeks, making the announcement in Vogue's September edition. The 40-year-old, 23-time Grand Slam champion said "it's the hardest thing that I could ever imagine." The four-time Olympic gold medalist shared on Instagram Tuesday that "the countdown has begun" and she will enjoy the next few weeks. Williams will end her career after the US Open – set to begin August 29 – to focus on building her family. Williams and Alexis Ohanian have been married since November 2017 and have one child together.