LONDON - The ballet world is spinning after one of the art's brightest stars walked away from Britain's Royal Ballet without explanation, days before he was due to take the lead in a new production.

Ukrainian dancer Sergei Polunin announced this week that he is quitting immediately. He had been due to open as Oberon in "The Dream" next week.

The 21-year-old has thrilled audiences since he became the company's youngest-ever principal dancer at the age of 19.

Royal Ballet director Monica Mason said Polunin's resignation had "come as a huge shock."

While ballet websites swirled with speculation that Polunin might have been poached by a rival company, there was no word from the dancer.

His Twitter biography on Thursday read "principal dancer of ?"