A schoolboy sent a naked picture of a married teacher to friends because he thought it would be a "laugh," a court heard.
The 15-year-old told Aylesbury Crown Court on day four of Kandice Barber's trial he thought sending the image to friends would be a "bit of a laugh."
But it fuelled rumours that Barber, 35, from Wendover in Buckinghamshire, was having sex with the pupil, rumours headteacher Nicholas Simms had heard from a teacher, the court heard.
Simms told the court the boy initially denied the rumours but said the lad later confessed as his friends told him to "tell the truth."
It is alleged Barber and the victim had sex with the pupil on three occasions in late 2018 – once in a field, second in woodland, and third in her 4x4 car.
A jury of seven women and five men at Aylesbury Crown Court heard testimonies from more of the now-17-year-old's friends and the headmaster of the school on Friday.
Mr Simms, who was headteacher at the school in Buckingham, said Barber had come to his office on March 11 for the second time.
The first had been on January 24 after Mr Simms heard from a teacher who had overheard a student speak of the rumours.
Mr Simms, went on to read a letter he had received from Barber after the initial meeting, which read: "Dear Mr Simms, I am writing to confirm that the rumours are completely not true.
"Being both married and having children in the school, this has been sickening and upsetting. The school means so much to me."
The boy was then asked back to the office in March to write a statement denying the rumours, and spent two to four minutes on it before coming back to Mr Simms and said: "My friends told me to tell you the truth."
A jury heard how the boy then described having alleged sexual activity with Barber, following a sports presentation evening in September 2018.
After the exchange, Barber was said to have borrowed his mobile phone to add herself to his Snapchat, which led to their alleged mid-October sexual encounter.
Mr Simms told the jury the boy was "visibly upset, his hands were shaking and it took him a long time to explain himself."
The headmaster said he then took advice from a local officer who specialises in safeguarding and called the police.
Barber was arrested on the morning of March 12 following the call and was taken into custody.
Defence lawyer Nadia Chbat, cross-examining Mr Simms, said "You didn't have any conversation with Miss Barber at all about the topic. The only conversation you had with her about this was on January 24."
A police interview of a close friend of the complainant was shown to the jury earlier this morning, in which the boy said: "I am 100% of one time it happened.
"They met up after but I'm not sure if they did it again after that," he said.
The jury heard excerpts from the school's official guidelines for staff behaviour with students.
It said: "Staff should never seek to make contact with a student outside of school."
Barber denies the child sex offences, and the hearing continues.