Former Ledyard High School English teacher William C. Friskey pleaded guilty Friday in New London Superior Court to having an illegal sexual relationship with a student. 

Friskey, 36, will be sentenced Feb. 25 to two years in prison, with a minimum mandatory of nine months to serve, for second-degree sexual assault. He will be on sex offender probation for 15 years following his release and will be required to register as a sexual offender. 

Friskey has been free on a $75,000 bond since he was arrested June 30. He has attended court several times while his attorney, Peter D. Catania, and prosecutor Theresa Anne Ferryman worked out a plea agreement. 

Friskey had worked for the school district since 2007. He resigned two days after he was arrested by town police. 

According to an arrest warrant affidavit, Superintendent Cathy Patterson called police on June 10 to report that a possible inappropriate relationship between a teacher at Ledyard High School and a female student had been brought to the attention of administrators. 

Though the alleged victim, who was 17 at the time, was old enough to consent to a sexual relationship, it is illegal for school employees to have a sexual relationship with students. The relationship took place in and out of the school building, according to Ferryman, who said the victim is aware of the plea agreement.