Eurovision winner and former Irish Presidential candidate Dana Rosemary Scallon said her brother, who is accused of indecently assaulting two children, had been "cured" after going to see a priest, a court has heard.
The one-time MEP arranged treatment for her brother, John Brown, following an allegation in the 1970s.
Mr Brown is facing five charges of indecent assault against two children.
One of his alleged victims told the opening day of his trial in England that she was reduced to tears when he crawled on top of her when she was a young child.
The alleged victim, who cannot be named for legal reasons, said he had told her not to tell anyone of what had happened and it was their "little secret" when the first incident occurred.
Mr Brown (60), of Lilly Hill Road, Bracknell, Berkshire, denies the charges against him and denies that the conversation about treatment between the mother of one of the victims and his sister ever took place.
Outlining the prosecution case to the jury yesterday, barrister Claire Howell said that the first alleged victim had confided in her mother that she had been assaulted by Mr Brown.
The mother had then phoned Ms Scallon, who had said that she would find treatment for her brother, the jury was told.
Ms Scallon subsequently told the mother that he had been "cured" after being seen by a priest, Ms Howell said, and they agreed not to tell the victim's father.
The first of the two alleged victims – against whom two of the indecent assaults are said to have happened – took to the stand yesterday.
When defence barrister Martyn Bowyer suggested that the conversation between her mother and Ms Scallon did not take place, she said: "Sorry, but it did."
The initial assault on the US citizen, who is now in her 40s, is said to have happened at a house in Wembley in London when the woman was between five and seven years old.
Another is alleged to have happened in a house in Torquay when she was aged between eight and nine while visiting Ms Scallon who was based there for a summer season at the peak of her fame.
She also alleged that he assaulted her twice in her home in the United States while Mr Brown was visiting.
These allegations are not included in the case as they happened outside the jurisdiction.
On the first occasion, Mr Brown is said to have crawled into bed on top of her and put his hands into her underwear which "felt very inappropriate", she told the court.
"I was little. I was more in shock. I didn't know what to do," she said.
On the second occasion, she claims he asked for a "wee hug" and rubbed his body up against her and pushed her towards a wall. Before this, she said she told another girl that she did not like the way he gave hugs. The final two times are said to have happened in her home in Iowa when he came to visit.
On the first occasion, he was minding her one evening when she went to bed, she said. She pretended to be asleep but he got on top of her and began thrusting on her as if having sex, she said. She then told her mother, who believed her.
On the final alleged occasion, she claims he tried to put his fingers inside her shorts but she reacted and hit him, threatening to cut off his privates.
When Mr Brown's sister Dana Scallon appeared on TV saying the allegations were lies during the Presidential campaign, she reacted with anger. She has now lodged defamation proceedings against TV3, RTE and Ms Scallon in Dublin.
The last three alleged indecent assaults are said to have happened to another woman, who was under 16 at the time, in Northern Ireland and Romford in Essex.
Barrister Claire Howell told the jury that Mr Brown had apologised to the first alleged victim and had confessed to his brother.
John Brown is charged with five counts of indecent assault against two children, one of whom was under the age of 13 and another under the age of 16, during the 1970s. One assault is alleged to have happened in Northern Ireland.
The accused man was a member of Dana Scallon's election team when she ran for the Presidency against Michael D Higgins in 2011.