Lorenzo told reporters in Valencia: "I've always thought there are four significant days in the life of a rider - the first one is when it's your first race, the second one is your first win, then your first world championship - not everyone can win the world championship, but some of us made it. And then the day you retire.
"As you all imagine here, I'm here to announce that this day has arrived for me.
"This will be my last race in MotoGP and at the end of the race I will retire as a professional racer."
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