The jury in the Jodi Jones murder trial has heard evidence from a girl described as a look-alike for the dead Midlothian teenager.
Mr Mitchell has denied murdering 14-year-old Jodi
Kimberley Thomson told the jury she had been the girlfriend of Luke Mitchell, the youth accused of murdering Jodi.
The High Court in Edinburgh heard that Miss Thomson, 15, met Mr Mitchell a year before he is alleged to have killed Jodi Jones.
He denies killing the 14-year-old schoolgirl in Dalkeith in June 2003.
Earlier during Thursday's proceedings, supermarket worker Robert Gilhooly, 17, who was described as a friend of Mr Mitchell's, said he had seen a photo of Miss Thomson and thought it was Jodi.
He told the jury that Mr Mitchell, 16, had also remarked on the likeness.
Mr Gilhooly said: "He mentioned that they looked alike. He said they were almost identical."
Miss Thomson said that when she read about Jodi's death and the fact that Jodi had been Mr Mitchell's girlfriend, she was annoyed.
She said: "I was upset. I knew he had obviously been cheating on me."
Miss Thomson, from Kenmore, in Perthshire, said she got to know Mr Mitchell during the summer of 2002 when he came to her local area on holiday with his mother.
"He was a friend of my brother," she said.
Prosecuting advocate Alan Turnbull QC asked: "By the time the holiday had finished had you and he become friends?"
She replied that they were and added: "When he left, that was when we started dating."
When asked how she would describe her relationship with Mr Mitchell, she said: "Boyfriend and girlfriend."
The jury heard how Miss Thomson read about Jodi's death
Miss Thomson said they phoned each other and may have sent text messages as well.
Mr Mitchell visited Kenmore in the autumn of 2002 and Miss Thomson stayed at the Mitchell home in Dalkeith from Boxing Day until just after New Year.
The accused also visited her on St Valentine's Day 2003.
Miss Thomson said Mr Mitchell was supposed to visit her last summer but this was "cancelled".
The teenager believed the visit was due to have been the weekend before Jodi was murdered but, when questioned about whether it could have been later, she said she could not remember.
Miss Thomson said she considered herself to be Mr Mitchell's girlfriend last summer.
Recalling how a friend showed her a newspaper article after Jodi's murder, she said: "Luke's name was in it and Dalkeith as well.
"His girlfriend had been murdered, or something like that."
Mr Turnbull asked if she had sent a text message to Mr Mitchell demanding an explanation.
"I cannot remember," Miss Thomson replied.
The court earlier heard of a six-hour police interview with Luke Mitchell where he was asked why he had not contacted Jodi when she failed to turn up to meet him as arranged.
Detective Sergeant George Thomson told the court Luke Mitchell had told them that he thought Jodi had met somebody else and had gone off with them.
But prosecutor Alan Turnbull QC put it to him that: "These two youngsters had met up every night, if they could, and she had only once before failed to keep an arrangement."
Sgt Thomson replied: "That is correct."
It has been alleged that Mr Mitchell attacked Jodi in woods near Roan's Dyke on 30 June, 2003.
He has denied that and claims that at the time he was in, or near, his home, and that Jodi was murdered by person or persons unknown.
He has also denied charges of possessing knives in public places and being concerned in the supply of cannabis resin to other school pupils, including Jodi.
The trial continues.