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 but the moment capped a 180-degree turn in their once pointy rivalry.

Maria Sharapova has entered the International Tennis Hall of Fame, with Serena Williams introducing her at the ceremony on Saturday night.

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