During more than two years of sexual abuse, the singer, now aged 55, encouraged the girl to call him "Daddy" and dress in a school uniform, the jury at Bristol Crown Court was told. He was accused of using the "besotted" fan "to feed his own sexual appetite".
It was also revealed in court that the woman making the allegations, who is now aged 34, will be paid pounds 25,000 by the News of the World if the pop star is found guilty. She has already been paid pounds 15,000 by the newspaper for stories of her 12-year relationship with the singer and is employing the publicist Max Clifford.
John Royce QC, for the prosecution, said the singer, who is charged under his real name of Paul Francis Gadd,was first introduced to the girl in 1976 when she was 11 while he was appearing at the Bristol Hippodrome.
The girl, who cannot be named for legal reasons, met Mr Gadd again in 1980. Shortly afterwards, she was subjected to the first in a series of sexual assaults, the court was told.
Mr Gadd faces four charges of indecently assaulting an under-age girl. He also faces four charges of serious sexual assault against the girl.
All the offences are alleged to have taken place between March 1980 and June 1982. The girl was aged 14 at the time of the earliest alleged offence.
In the dock, the singer, wearing sunglasses and diamond-stud earrings, cupped his hand to his ear to hear the proceedings and leant forward to plead "not guilty" to all charges.
Mr Royce said: "We say this idol has feet of clay. He has used this fan to feed his own sexual appetite. He did so with a young girl who was so enthralled he felt he could do what he wanted outside the law."
The court was told that the second time the girl met Mr Gadd was at a concert near Loxton, Somerset, on Valentine's Day 1980.
"He pulled me out of the audience and he sang a song to me. I think it was It Takes All Night Long," she told the court.
"After the show he came back and spoke to my parents ... I was just besotted, he was talking to us and made friends with us. My mum asked him whether he would like to come back for Sunday lunch. He did ... he stayed for five days ... I was in shock. The man on my bedroom wall was in my living room," "
Mr Royce said the sexual relationship between Mr Gadd and the girl started after the singer began making regular visits to her family home at Burnham- on-Sea, Somerset.
The first charge of indecent assault relates to an occasion in 1980 when the girl was staying with the singer at a house in Banbury, Oxfordshire, said to have belonged to one of Mr Gadd's relatives. Mr Gadd, who was aged 35 at the time, allegedly kissed the girl and performed a sexual act.
Mr Royce told the court that Mr Gadd had threatened to commit suicide if the girl finished their relationship.
The woman said: "He wanted me to call him `Daddy'." She said Mr Gadd kept a school uniform in his wardrobe and would ask her to put it on.
Mr Royce said the girl continued to be obsessed with Mr Gadd and he convinced her that he was serious about the relationship.
He added: "The relationship carried on for a substantial number of years. It had its early regular ups and downs and he remained very much the dominant partner."
The woman said their relationship ended in 1991 when she was about 26 years old.
Questioned by Trevor Burke, for the defence, the woman agreed she had been paid pounds 15,000 by the News of the World for two stories of her relationship with Mr Gadd. The court was told that she employed the publicist Max Clifford and signed a contract with the newspaper within days of hearing of Mr Gadd's arrest at a computer store in Bristol in November 1997. Mr Burke told the jury that the woman could be paid a further pounds 25,000 by the News of the World if Mr Gadd was convicted. The woman become more and more upset as Mr Burke accused her of making up her allegations to secure mone. As he finished his cross-examination, she turned to Mr Gadd, sobbing and said: "Tell him, tell him, please."
Under re-examination by Mr Royce, she said: "My motive was to tell people the truth, to let them know ... I understand now that people cannot do that to children. That's wrong."
The case continues today.