Williams' surprise appearance to induct Sharapova was "months in the making" and required the code name of another female icon.

When Sharapova was inducted into the Tennis Hall of Fame on Saturday night, her former on-court antagonist provided the introduction. For many tennis watchers, Williams’s top secret cameo was shocking,

Sharapova was honored with an official U.S. Open ring Sunday at Arthur Ashe Stadium, following her induction into the International Tennis Hall of Fame. She accepted her latest hardware in the latest rendition of the tennis dress that changed the sport. “New York City, what a special place and special court,” Sharapova said.