A married teacher who has admitted having sex with an underage student in her Florida classroom told the teen she wanted to leave her husband for him when he turned 18, according to new court documents.

Heather Mashburn-Smith, 37, gave a “full, post-Miranda confession” about having sex with the boy — while admitting she knew he was “just a teenager,” according to her arrest affidavit seen by WBBH-TV.

The pair had chatted over Snapchat — with it turning flirtatious after the 17-year-old student told his teacher she was “pretty,” according to the docs.

The teen started making extra trips to Mashburn-Smith’s classroom in Port Charlotte High School, where they eventually kissed — and had sex at least twice, according to the affidavit. 

During the disturbing trysts, the teacher complained about her marriage — and told the boy she wanted to leave her husband for him when he turned 18, the legal age of consent in Florida.

That concerned the boy, who stopped chatting and blocked his teacher — who kept messaging him on Snapchat, according to the affidavit.

Mashburn-Smith then admitted it all to cops, saying that she “made a mistake,” the docs said.

She admitted she knew the student was “just a teenager” but said he made her feel desired, officers said.

The educator was charged with of unlawful sexual activity with minors, which carries a maximum sentence of 30 years in prison.

“What this woman has done is not just unlawful, it is damaging to the students and staff around her,” Charlotte County Sheriff Bill Prummell said.

She was also suspended from Port Charlotte High School, the district said.

“The actions of this individual are a direct violation of the duty every educator owes to students and families,” Charlotte County Public Schools Superintendent Mark Vianello said in a stern statement.

“We will not tolerate anything that compromises student safety. This individual has been placed on administrative leave as we work closely with law enforcement and pursue full accountability,” he added.

“What this woman has done is not just unlawful, it is damaging to the students and staff around her,” Charlotte County Sheriff Bill Prummell said of the teacher, who now faces up to 30 years in prison.