LONDON (AP) — A former English National Ballet principal dancer was convicted Tuesday of sexually assaulting young female dance students.

Yat-Sen Chang, 49, was found guilty of 12 counts of sexual assault and one count of “assault by penetration.” The offenses took place at the English National Ballet and Young Dancers Academy in London from 2009 to 2016, and relate to four teens who were between 16 and 18 years old at the time.

The victims accused Chang of touching them inappropriately during massages at the schools. During the trial, Chang said he had “no idea” why the allegations were made against him, and said he hadn't touched any of the complainants in an inappropriate or sexual way.

But prosecutors described Chang as an internationally renowned ballet dancer who used his position to commit sexual offenses against young students he taught.

“Yat-Sen Chang used his position as a famed and trusted ballet teacher to groom and sexually assault teenage dancers under his training,” senior prosecutor Nahid Mannan said. “At 20 years their senior, Chang would have been well aware that his conduct was grossly inappropriate and predatory.”

The jury convicted Chang, who was born in Cuba and now lives in the German port city of Kiel, after 13 hours of deliberations.

He was remanded in custody to be sentenced on June 18.