Roger Federer suffered a knee injury in January that required surgery and the mystery surrounding that injury was exactly how it happened. He finally answered that question while speaking to reporters on Thursday, March 24.

The Associated Press noted that the tennis star revealed that his injury occurred in his bathroom while he was getting his twin daughters ready for their bath.

"It was a very simple movement, probably a movement I've done a million times in my life," he said. "I didn't think much of it when it did happen."

But as it turned out Federer’s knee became swollen and doctors told him he actually needed surgery, so for the first time in his career he underwent an arthroscopic procedure.

"When I woke up and looked at my knee it was like, 'This doesn't feel like my leg. I can't believe I did the operation and I hope it will come back from here.' That's when I got scared,” he said. “Then literally one day, two days later I had no more pain."

The 34-year-old 17-time Grand Slam winner is now making his return to the court and will face 2009 U.S. Open titlist Juan Martin del Potro in Miami on Friday.