Dawn Giannini, 49, a Palo Alto elementary school teacher faces 24 felony charges involving sexual misconduct with a minor

A teacher from California who is the wife of a US Army Lt Col has been arrested and charged with incest after a pupil recognized the teacher as appearing in a video on a porn website.

The student noticed the youngster in the clip was a classmate and as underage female family member, it is claimed.

The teacher, who is a mother-of-two, Dawn Giannini, 49, from Palo Alto remains in custody while the investigation continues.

The teen who spotted the teacher in the raunchy clip online had been looking at PornHub.

They then alerted the school's principal, who called police, which resulted in Giannini's arrest.

Giannini who is married to Thomas, a US Army Lieutenant Colonel, and one of the most senior positions in the Army, was a fourth grade teacher at St. Elizabeth Seton Catholic School in Palo Alto, in 2015.

Dawn Giannini, 49, pictured with her husband, Thomas, a US Army Lieutenant Colonel, was booked into Redwood City jail

Back in the good old days: Dawn is pictured with her husband, Thomas, a lifelong military man

Before that, she was a special education assistant and substitute for the Redwood City School District.

Redwood City School District Superintendent John Baker sent out an email to parents about Giannini and said while it is believed she did not assault a student, the information is still 'truly heartbreaking.'

San Mateo County District Attorney Steve Wagstaffe would not identify how Giannini and the young girl, who was 14 at the time of the crimes, were related.

Giannini is accused of having a sexual relationship with the underage family member from November 2014 until November 2015.

Giannini is alleged to have recorded some of the sexual interactions, which were then later uploaded onto the PornHub website.

Prosecutors believe the girl posted the video.

Giannini is currently being held on $1.75m bond. The victim was not one of Giannini's students but a family member. She is pictured alongside husband Thomas, an Army Lt Col

The allegations will have brought shame on the family of four which include the Giannini's two teenage children.

Her husband, Thomas, is a high-ranking military officer who has had three overseas deployments to Iraq and Afghanistan.

He also has proven leadership experience as a company commander, Battalion Operations Officer and most recently as an Area Office Officer-In-Charge coordinating several Afghanistan Infrastructure Projects in remote locations, while serving in an active combat zone.

Investigators saw Giannini alongside a girl in a video that was uploaded online

His wife now faces two dozen charges including seven counts of lewd act on a child, six counts of oral copulation on a child under 16 years old, six counts of sexual penetration with a foreign object, one count of showing porn to a child and one count of incest.

'We know the victim was sexually active, and there were a lot of videos that were uploaded,' DA Wagstaffe said.

'We know that this occurred in at least two counties. It occurred here in our county, in Redwood City and there was a trip down to Santa Cruz that she took with the victim and there was sexual activity there.'

It is not believed that Giannini acted inappropriately with any of her students, however the DA is still investigating all aspects of the case.

Giannini has since been fired from the Redwood City School District and will not be able to work at the district ever again.

She appeared in court on Thursday and did not enter a plea, Wagstaffe said. She remains in jail in lieu of $1.75 million bail.

If anyone has any information about the case, they are asked to call Redwood City Police Detective Ryan Kimber at (650) 780-7138.