Sinn Fein president Gerry Adams has told a court his brother, Liam Adams, admitted sexually abusing his daughter.
Liam Adams is charged with 10 counts of sexually abusing his daughter Aine, who has waived her right to anonymity. He denies all the charges.
Giving evidence at the trial in Belfast, Gerry Adams said that he had several walks with his brother.
He said during one of them, Liam Adams acknowledged he had abused Aine, but said that it had only happened once.
The Sinn Fein president said that Liam Adams made the alleged admission during a long walk in the rain in Dundalk, County Louth, in 2000
"I had a long walk with Liam. We had a number of conversations," Mr Adams said.
"During the course of that he acknowledged that he had sexually abused Aine. He said it only happened the once."
Mr Adams was asked what Liam Adams had said he had done.
Gerry Adams replied: "To the best of my recollection the terms that he used were that he had molested her or that he had interfered with her, that he had sexually assaulted her."
Mr Adams said he had first confronted his brother about the alleged abuse during a meeting in Buncrana, County Donegal, in 1987. He told the court that at that time Liam Adams denied the allegations.
Mr Adams said that when the conversation concluded he spoke to his brother telling him "this was a very serious situation, that he had to reflect on and to acknowledge what she (Aine) was saying, that she had no reason to make any of that up".
He added later that he had two further meetings with his brother Liam, "one in my home, and one day walking in the Falls Park".
Later, the defence barrister suggested that the alleged admission had not taken place.
"You say that your brother made an admission to you in 2000 walking in the rain in Dundalk. I should make it clear to you that I suggest no such admission was made," she said.
Gerry Adams replied: "I don't accept that but I understand it."
Under cross examination, Mr Adams said that initially he knew nothing of his niece's specific claims of rape against her father and that this remained the situation "for 20 years".
Mr Adams told the court that he "did have a problem with exact timelines" for events, but denied that he had lied to a journalist about his brother in an effort to distance himself from him.
"I take exception to you saying it was a lie," Mr Adams told Ms McDermott, who repeated later that "again I take exception" to being accused of lying, in his interview with the journalist.
Liam Adams, 57, from Bearnagh Drive, Belfast, denies 10 charges of sexually abuse, including rape, indecent assault and gross indecency, against his daughter between 1977 and 1983.
The trial continues.