REIGNING MOTOGP CHAMPION and 2012 leader Casey Stoner has announced he will retire from the sport at the end of the year.

The 26-year-old Australian, who won the MotoGP world title in 2007 and 2011, cited rule changes as a major factor behind his decision.

“This sport has changed a lot and it has changed to the point where I am not enjoying it,” Stoner said during preparations for Sunday’s race in Le Mans, the fourth round of the campaign.

“I don’t have the passion for it and so at this time it’s better if I retire now.

“There are a lot of things that have disappointed me, and also a lot of things I have loved about this sport, but unfortunately the balance has gone in the wrong direction.

“And so, basically, we won’t be continuing anymore.”

At the Portuguese MotoGP earlier this month, Stoner denied reports he had decided to quit.

But speaking on Thursday, the Honda rider performed a dramatic U-turn to confirm the rumours.

“After a long time thinking, a lot of time talking with my family and my wife, this has been coming for a couple of years now but at the end of this 2012 season I will be not racing in the 2013 championship,” Stoner said.

“I will be finishing my career at the end of this season in MotoGP, and go forward in different things in my life.”

Stoner started his MotoGP career in 2006 after finishing second in the 250cc World Championship the previous year.

He raced for LCR in his debut season, before joining Ducati in 2007.

Stoner, who has 35 race victories from 103 attempts, joined Repsol Honda ahead of the 2011 campaign.

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