(CNN) -- Reigning MotoGP world champion Valentino Rossi is to leave Yamaha at the end of the current season and has signed a two-year deal with Ducati.
The 31-year-old Italian superstar has been with Yamaha for seven years, winning four world titles, but said he wanted a "new challenge" with Ducati.
"It is very difficult to explain in just a few words what my relationship with Yamaha has been in these past seven years," said Rossi in a statement released Sunday.
"The time has come for me to find new challenges; my work with Yamaha is now finished.
"Sadly, even the most beautiful love stories come to an end, but they leave marvelous memories," he added.
Rossi, who finished fifth in Sunday's Czech Grand Prix, is out of this year's title race having been sidelined for six weeks after breaking his leg at Mugello.
He will replace Australia's former world champion Casey Stoner, who will go to Honda after four years with the Italian-based team.
Current world title leader Jorge Lorenzo is set to be joined by promising young American Ben Spies at Yamaha next season.
Lin Jarvis, managing director of Yamaha Motor Racing, paid tribute to the departing Rossi.
"I would like to express our sincere gratitude for the amazing seven years that we have spent together," he said.
Rossi joined Yamaha from Honda in 2004 when they were a mid-ranking team and has helped turn them into the most formidable works team in MotoGP.
"We are delighted to announce that Valentino Rossi will be with us from 2011," said Ducati president Gabriele Del Torchio.
"He is a paragon of excellence in the world of motorcycling."
Rossi has won 10 world titles during his remarkable motorcycling career, seven of them in the MotoGP category.