Victim's brother made threats to Rolf Harris

Veteran Australian entertainer Rolf Harris, centre, who is accused of indecent assault, accompanied by members of his family as he arrives at court. Photo / AP

A brother of Rolf Harris' main accuser says he threatened the entertainer with "physical violence" after learning of his sister's sexual abuse but the Australian simply replied "it takes two to tango".

The older brother only found out about the alleged abuse 20 years after Harris first assaulted his then 13-year-old sister in 1978, he told Southwark Crown Court on Wednesday.

The mid-1990s revelation came after the man confronted his sister one Sunday lunchtime over her heavy drinking and obnoxious behaviour.

The brother then rang Harris.

"I threatened physical violence," the man, now in his early 50s, said.

"I told him why I was angry. I said: 'You abused my sister sexually.'

"He said 'It takes two to tango'."

The 84-year-old admits to having a sexual relationship with the alleged victim - his own daughter Bindi's childhood friend - but insists it only started after she was 18.

The complainant's elderly mother was also in court on Wednesday.

She told the jury she was "completely amazed" in the mid-1990s when her daughter revealed Harris had abused her.

The mother had let the children's entertainer be alone with her only daughter because she trusted him.

"(But then) she told me she'd been abused all her life which made me very angry," she told the court.

"I was completely amazed."

The complainant's mother spoke to Harris's wife, Alwen, a few weeks or months after learning of the abuse.

Alwen wasn't in court on Wednesday for the first time.

Defence lawyer Sonia Woodley QC suggested Harris never went upstairs at the complainant's family home, which is where the crown alleges some of the seven indecent assaults took place.

But the victim's mother insisted: "He did."

Her father said she he was "absolutely devastated" when he found out she'd been abused.

He was "very, very angry" with Harris and wrote to him expressing his disgust.

The entertainer wrote back apologising for betraying the father's trust but insisting there was no physical relationship until the alleged victim was 18.

"When I see the misery I have caused (her) I am sickened by myself," Harris wrote in 1997.

Her father on Wednesday said the entertainer's argument that nothing happened while his daughter was underage "was rather at odds with the content and tone of the rest of the letter".

The complainant's other brother - the eldest - also took to the witness stand.

He said his little sister rang him two or three years ago to discuss whether she should finally go to the police.

She told him she felt ready and that reporting Harris would be "part of reclaiming her life".

A school friend said the alleged victim told her, when both girls were about 16, that Harris was a "dirty old man" who had "touched her up".

Some 16 years later in 1996 she urged her friend to report the matter but at that stage she wasn't ready because she feared "a media circus".

It was during this period the woman sought help for the drinking problem she blamed on Harris.

The prosecution on Wednesday read out statements from five medical professionals who said the complainant had told them she'd been abused by the artist and singer from the age of 13.

They said she'd been reluctant to reveal details.

Harris is accused of indecently assaulting four girls, one as young as seven or eight, between 1968 and 1986. The 84-year-old denies all the charges.

- AAP