Serena Williams is moving on from the sport she's dominated for decades -- the superstar just announced she's "evolving away" from tennis after the U.S. Open.
The 40-year-old shared the news in an essay with Vogue on Tuesday ... saying it's time to move on and focus on other challenges -- raising a family and business ventures off the court.
"I’m terrible at goodbyes, the world’s worst," Williams said. "But please know that I am more grateful for you than I can ever express in words.