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Mayweather Jr. and Bieber celebrate Mayweather's victory over WBC/WBA 154-pound champion Alvarez at the MGM Grand Garden Arena in Las Vegas, Nevada

Floyd Mayweather Jr. (L) and singer Justin Bieber celebrate Mayweather's victory over WBC/WBA 154-pound champion Canelo Alvarez (not pictured) at the MGM Grand Garden Arena in Las Vegas, Nevada, September 14, 2013. Alvarez was previously undefeated in 42 fights. REUTERS/Steve Marcus (UNITED STATES - Tags: SPORT BOXING ENTERTAINMENT)