Usain Bolt will have to hand back one of his nine Olympic gold medals after Jamaican team-mate Nesta Carter tested positive for a banned substance.

Carter was part of the Jamaican quartet that won the 4x100m in Beijing in 2008.

His was one of 454 doping samples retested by the International Olympic Committee (IOC) last year, and has been found to contain the prohibited substance methylhexaneamine.

Carter, 31, was also part of the squad that won the event at London 2012.


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