A New Jersey P.E. teacher is behind bars after a former student revealed he had a sexual relationship with her that spanned all four years of his time in high school.

Bridgewater-Raritan High School teacher Lydia Pinto, 38, is facing one count of first-degree aggravated sexual assault and two counts of second-degree sexual assault in connection with the case, according to the Somerset County Prosecutor’s Office.

Authorities learned of the four-year tryst on October 16th, when they received an anonymous letter that detailed the relationship, according to the Bridgewater Police Department. That prompted detectives to interview the victim, who’s now an adult, prosecutors say. “The victim reported engaging in a relationship with former teacher, Lydia Pinto,” reads a statement released by the Prosecutor’s Office. “The victim further reported that the relationship turned sexual when the victim was between the ages of 14 to 15 and continued until the victim’s senior year of high school.”