A teacher in the Northwest Independent School District is facing charges for allegedly having sex with a student, according police.

A Denton County arrest warrant affidavit details the alleged relationship that developed between teacher Katherine Harper and a 15-year-old boy between June 1 and July 31, 2016.

The investigation started after an anonymous tip in December to Byron Nelson High School.

Harper was a former tennis coach and teacher of the student at Tidwell Middle School.

Investigators said they found Harper and the teenager exchanged multiple explicit text messages, including nude photos, during the months of June and July of last year.

According to the affidavit, the two had five sexual encounters and had sexual intercourse three times.

Harper was arrested by the Trophy Club Police Department and charged with a felony of improper relationship with a student.

The Northwest ISD released the following statement Thursday:

"Northwest ISD administration is aware of the investigation involving a Tidwell Middle School teacher. When the district learned of the allegations, an investigation was conducted, and the teacher was placed on administrative leave. The district notified authorities and cooperated with Trophy Club Police Department during their investigation.

"Northwest ISD and all campuses are committed to the safety of its students and staff. At the time of hiring, all teachers and staff undergo thorough state and national background checks, including fingerprinting."