A veteran of Opera Australia's chorus stared unflinchingly at the judge as he was sentenced to three years in prison for the historical sexual assault of a 14-year-old girl.

Key points: Lewis was a member of the Opera Australia chorus and met the girl when she joined the national opera company's children's chorus

Lewis was a member of the Opera Australia chorus and met the girl when she joined the national opera company's children's chorus The victim formed a friendship with Lewis and became infatuated with the tenor, who was 20 years her senior

The victim formed a friendship with Lewis and became infatuated with the tenor, who was 20 years her senior The two often spoke on the phone and attempted to conceal their relationship by referring to it as "chocolate"

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David Edward Lewis pleaded guilty in March to two counts of sexually assaulting the victim — who cannot be named — between 1993 and 1995, while they were both employed by the national opera company.

At his sentencing, the Sydney District Court heard that Lewis was married, in his thirties and an established member of Opera Australia's chorus when he met the girl, a talented singer who had been chosen to join the Opera Australia children's chorus.

The victim formed a friendship with Lewis, during which she confessed to having suffered previous sexual assaults.

She became infatuated with the tenor, who was 20 years her senior.

In sentencing, Judge Sarah Huggett said the assaults typically took place backstage and involved kissing and mutual masturbation.

They often spoke on the phone and attempted to conceal their relationship by referring to it as "chocolate".

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Children's manager appointed after discovery

It was during a season of an Opera Australia production that Lewis took the victim to his house while his wife was away and assaulted her in the spa.

David Lewis (left) departing court from an earlier appearance in January. ( ABC News: Liv Casben )

During another production at Sydney Opera House, they were discovered in a sexual act by the company's dance captain and ballet master.

After the discovery, the victim ran back to rejoin the other children in the cast who had laughed at the fact Lewis's heavy black makeup was smeared on her.

After that discovery, Opera Australia appointed a children's manager.

A spokeswoman for Opera Australia told the ABC it had cooperated fully with the police, but had been unable to locate any official record of the incident.

She said the company would not be making any further comments at this time.

Judge Huggett said, "I have no doubt [Lewis] is remorseful in so far as it affects himself".

She found "he deliberately took advantage of [the victim's] relative emotional immaturity".

Judge Huggett said Lewis had apologised to the victim many years later, but "the offending only stopped because the offender was caught, not because he realised the inappropriateness of his conduct".

Lewis, 59, was taken immediately into custody after the sentencing.

His victim watched intently as he surrendered his watch, removed his belt and was escorted from the court.

Lewis was a stalwart of the national opera company for 29 years, a singer employed full time to perform in the chorus who was occasionally promoted to senior roles after 2010.

He took long service leave after he was charged in July last year and later resigned.

The court heard he has since been dependent on the Newstart allowance.

His final roles were as the Emperor in Turandot on Sydney Harbour in 2016 and Pedro in Two Weddings, One Bride in 2017.

The judge found Lewis had a low risk of reoffending and moderate to good chance for rehabilitation.

Judge Huggett noted he had no other history of offences.

He will serve at least two years and be eligible for parole in 2020.