A Florida math teacher has been busted for allegedly having sex with a student – and their illicit fling was uncovered when her alleged victim lied to his parents.

Kirsten Rose, 37, was arrested Friday – five months after she started chatting with the boy out of class on Instagram, according to court docs seen by WPEC-TV.

They continued chatting into the new year and allegedly had sex in February and March, with the boy’s parents becoming alarmed when he returned home late from work one night.

They realized that his location was at an unfamiliar home, and when challenged, he replied he was with his “girlfriend,” without naming Rose.

The boy’s parents continued to question him and the illicit tryst was exposed when he admitted he was in a relationship with his teacher.

Rose, who taught at Cocoa Beach Jr/Sr High School, was charged with five counts of unlawful sexual activity with a minor and is being held without bond at the Brevard County Jail following a police probe.

Her arraignment is set for May 5 and the investigation remains ongoing.