Serena Williams has never let pain or injury stop her from playing the sport she loves—she has even played while pregnant! As a result, many fans may not know that the tennis legend secretly endured one of the most debilitating conditions in her pursuit to win her many titles. Williams, a 23-time Grand Slam winner, has struggled with migraine attacks since her 20s.

Williams’s migraine headaches became daily occurrences amid the coronavirus pandemic, making it much harder to handle, People reports. “It’s all incredibly stressful,” Williams said. “I was dealing with a lot of stress and unknown factors and things that I wasn’t used to, and so I think that was contributing to my migraine attacks and making them more frequent.”

Williams’s migraine attacks were fairly manageable when they were sporadic. According to the athlete, she often played in agony because the pain was hard to explain to those around her, including her father, who was her coach. People would tell her to “tough it out” because, unlike a knee injury, a migraine isn’t a visible ailment.

But Williams reached a point where she could no longer mask her pain. During quarantine, she trained and spent a lot of quality time with her daughter. By day’s end, she would experience long-lasting headaches. In addition, living in Florida exposed her to abundant sunlight, which can trigger migraine attacks.

Finally, she visited her doctor, who prescribed Ubrelvy, a pain and symptom reliever for migraine. The drug helped relieve Williams’s migraine so effectively that she became a spokeswoman for the med.

Now free of migraine pain, Williams is excited and confident to continue training for the upcoming U.S. Open in New York City, which will be played without fans due to the coronavirus pandemic. “I’ve always played with a such a big crowd,” she said. “Without fans, how will I do? I don’t even know. But I look at it as another experience. A wild experience.”

However, now one thing is certain, Williams won’t have to worry about playing through another migraine attack.

For related coverage, read “NFL Legend Terrell Davis on His Lifelong Battle With Migraines” and “New FDA-Approved Drug Could Stop the Onset of Migraines.”