A private detective who was hired to follow a man’s was shocked to discover her having sex with his OWN son.

Amber Telford, 33, last week pleaded guilty to unlawful sexual activity with a minor after she was caught out having sex with a 17-year-old boy.

Telford’s husband had hired the PI to track his wife’s movements and the he found them lying naked together at the dance studio where Telford taught.

But the case took a surprising twist when it emerged that the teenager was the son of the private detective.

Telford and the unnamed teen began a sexual relationship after the pair grew close while Telford taught him at Colette’s Dancing School in Taylorsville, Utah.

They began flirting and Telford paid for him to travel to Disneyland for a dance competition and bought new clothes for him.

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They soon became lovers and the pair are said to have romped in Telford’s car and home.

A court document stated: “She started by flirting with (the teen) and eventually began a sexual relationship with him that occurred at her home, her mother’s home and also in a vehicle belonging to Amber.”

The private detective discovered them under a blanket with their clothes “strewn all over the floor”.

Telford’s estranged husband had filed for divorce from her two months before the discovery of the affair.

She was jailed for 30 days and ordered to perform 150 hours of community service.

After her release, Telford must also register as a sex offender.

Pics: Facebook/Police handout