MotoGP champion Casey Stoner has announced that he will retire from the sport at the end of the season.
The 26-year-old Australian has revealed that a waning passion for racing led him to make the shock decision.
"This sport has changed a lot and it has changed to the point where I am not enjoying it," he told reporters.
"I don't have the passion for it and so at this time it's better if I retire."
The two-time champion currently leads this season's rankings by a single point.
