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Frank Stronach leaves a Toronto courthouse on June 19.Chris Young/The Canadian Press

A lawyer for billionaire businessman Frank Stronach says a judge has declared a mistrial on his sexual-assault conviction in a surprise ruling ahead of his scheduled September sentencing hearing.

Stronach was convicted last month of two charges, sexual assault and the historical offence of indecent assault, related to two complainants in a trial involving decades-old allegations.

Lawyer Leora Shemesh says the mistrial on the sexual-assault conviction was granted after she presented e-mails in court from the woman’s lawyer in a separate civil complaint that she alleged were inconsistent with testimony in the criminal trial.

The auto parts magnate initially faced 12 charges involving seven complainants, but by the time arguments in his trial wrapped up, prosecutors had withdrawn one charge and agreed Stronach should be found not guilty on four more.

In an interview, Shemesh called the decision to declare a mistrial after a conviction “incredibly rare.”

The Canadian Press has reached out to the prosecutor’s office for comment.