A teacher who had sex with a student who had sought his support entered her home through the side entrance to avoid her mother's Ring doorbell.
Ieuan Bartlett, 29, developed a sexual relationship with the girl while working as a trusted welfare officer.
Cardiff The Crown Court heard he also pressured her into sending him naked photos of herself.
Bartlett admitted to 12 counts of sexual activity with a child as a person in a position of trust, including having sex with the girl.
He pleaded guilty after a previous jury could not reach a verdict. Bartlett was supposed to stand for a new trial but changed his plea to admit to the sexual crimes.
Prosecutor Matthew Cobbe said in the previous trial that Bartlett was the teacher the girl had turned to for support in his role as a welfare officer, but he took advantage of that position.
Mr. Cobbe said: 'He gained her trust and confidence, and for the first few months of getting to know her, he built an even closer bond with her.'
'It is the prosecution's argument that he started a sexual relationship with her. This case is about that sexual relationship.'
Mr. Cobbe said the girl began meeting Bartlett alone at the high school where he worked.
'It was that privacy, that isolation that allowed the defendant to build on the bond he was creating, nurturing with her, ultimately causing her to believe that he had fallen for her and that she was in a loving relationship with him,' he said.
She was just 16 when he asked for explicit photos – and sex took place during the school holidays in August 2021.
The girl told the police that Bartlett would hug and kiss her, and tell her he wanted a relationship with her and to move in with her when she left college.
She told officers he would 'constantly say he loves me and loves everything about me' and that he wanted to book hotel rooms for them to have sex in.
The girl said she had unprotected sex with Bartlett at her home after the school term had finished for summer in August 2021.
He came and left through the side door of the house to avoid being recorded by the Ring doorbell camera, the court heard.
Bartlett was arrested and interviewed twice by the police but refused to answer any of the questions.
Initially, he denied any kind of sexual relationship with the student during the school term, but admitted that on August 15, after the school term had ended, he went to her house and had sex with her.
Mr. Cobbe said: 'The text messages put into context the relationship taking place between them and make it obvious it was a longer lasting sexual relationship.'
The prosecutor said Bartlett asked the girl for nude photos after the term had ended 'clearly stating to her what he wants despite her obvious reluctance'.
He added: 'She was 16 at the time, and his possession of those images was and is a crime regardless of whether they were shared or exchanged during the school term.'
The girl stated that she felt pressured to send naked pictures and would cry while sending photos of herself.
Defending Bartlett, Sophie Standard told the court that the previous trial had significant impact on his mental health and he was receiving counseling.
Bartlett, from Whitchurch, Cardiff, previously confessed to having an inappropriate picture of the girl.
Judge Lucy Crowther detained Bartlett in custody and he will next appear at Cardiff Crown Court for sentencing on Friday, May 3.
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