Tennis great Serena Williams has confirmed her decision to retire from the sport, calling it a reluctant decision and the hardest thing that I could ever imagine.

Im here to tell you that Im evolving away from tennis, toward other things that are important to me, she said in an essay for Vogue published Tuesday. Im torn: I dont want it to be over, but at the same time Im ready for whats next.

Williams, 40, did not specify an end date and said she intends to compete in the U.S. Open which will begin later this month in New York. She hinted on Instagram , however, that it could be her final tournament, writing: The countdown has begun, and, Im gonna relish these next few weeks.

The 23-time Grand Slam champion said she wants to focus on her family, including having another child with her husband, Alexis Ohanian. She also said she feels professionally driven by her venture capital firm, Serena Ventures, which she launched a few years ago.