A man used his "animalistic" sexual desires as a "justification" for allegedly raping his young niece, a court has heard.
"He was linking that to being unable to control his desires with [his niece] in his bed," the alleged victim's sister said on Thursday, the third day of an ACT Supreme Court trial.
Antonius van de Zandt, 72, denies making any such admissions, as well as charges of sexual intercourse with a child and committing an act of indecency on a child.
The former restaurateur admits he "sexually interfered with" his 15-year-old niece when they shared a bed in his Kaleen home in 1986, but claims he was "genuinely not awake" during the incident.
The alleged victim has given express consent to be identified in media reporting.
The woman's older sister detailed an "incredibly tense" meeting that took place, in the days following the incident, between her, the alleged victim's mother, van de Zandt and his wife.
In this meeting, it is alleged van de Zandt admitted he "touched" his niece's genitals and answered questions about why he had committed the act.
"[van de Zandt] was explaining in detail about his sexual desire and the strength of his sexual desire," the alleged victim's sister said.
"That was his response to the question: 'Why would you have done this?'
"It was more just justifying how it had happened."
The woman recalled her uncle, who denies the meeting ever happened, did not appear to be remorseful.
While she admitted to paraphrasing parts of the conversation that took place 37 years ago, the alleged victim's sister was certain van de Zandt used a version of the word "animalistic".
"I heard things that normally a person at 17 wouldn't hear about their uncle and aunty ... It was very distressing for me," she said.
The alleged victim's mother also gave evidence on Thursday, when she said she could not recall the meeting or many of the things allegedly said during it.
"This whole thing was very unpleasant and maybe your mind closes off," the mother said.
However, she did recall van de Zandt saying something about "this is the way I have sex with [my wife]", but could not place where she had heard the comment.
The alleged victim's mother also said she did not consider reporting the incident to authorities at the time.
"You didn't go to the police. You kept it secret," she said.
The court previously heard on Wednesday that van de Zandt spoke about the incident to an audience of "200 people" in 2004, when he joined his niece at a self-help course in Melbourne in 2004.
The trial continues.
