Both John Legend and the Roots performed at A&E Television Networks upfront party the other night at the IAC Building in Chelsea. But some guests thought John Mayer might also take the stage for a surprise performance. The rumor started when network president Abbe Ravin and Bob Saget chatted backstage with “a tall, good-looking guy” who looked like Mayer (pictured). But the mystery man was Mayer’s brother Carl, who works at a New York media firm. The real John Mayer is on tour in Australia.