Watch : Nicole Richie Seemingly Reacts to Hilary Duff’s New Song Amid Joel Madden RumorsHilary Duff knows that this is what dreams are made of. After all, as the "So Yesterday" singer hit all the right notes during her Aug. 5 sold-out show in New York City, she came clean about the surprise guest appearance: Her ex-boyfriend Joel Madden's band Good Charlotte. "I brought two of my dearest friends to New York City tonight. While fans waited with bated breath during the Lucky Me Tour stop, the pop star announced, "Can you please give the warmest welcome to my friends, Good Charlotte?" Joel—who dated the Disney alum, nine years his junior, from 2004 to 2006—and his brother Benji Madden stepped onstage to perform "The Anthem," with Hilary chiming in for an unforgettable duet.