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Harris abused the girl for her entire teenage and young-adult life, first assaulting her at the age of 13 as she got out of the shower, prosecutor Sasha Wass told the jury. He also took photos of her as she slept and molested her within yards of other sleeping children, she added.
A global star of family TV entertainment for more than 50 years, Harris is the biggest name to go on trial since British police launched a major investigation after revelations that the late BBC TV host Jimmy Savile was a prolific child sex abuser, leading to the arrest of more than a dozen ageing celebrities.
The 84-year-old is charged with 12 counts of indecent assault against four girls between 1968 and 1986, the youngest of whom was aged just seven or eight at the time of the alleged offence.
Harris denies the charges.
Giving evidence behind a screen, the woman, now aged 49, said she was too scared and intimidated by Harris's fame to tell anyone about the abuse and he routinely sexually assaulted until she was 28 years old.
"I was just so scared of him, He was this big man on the telly and I thought no one would believe me anyway," she said. "He was this huge character and I thought I wouldn't stand a chance.
"I felt disgusted in myself for letting him do it."
Wearing a dark suit, pink shirt and brightly coloured striped tie, Harris sat expressionless in dock at Southwark Crown Court as the woman described over 10 different occasions when, she said, he had assaulted her.
Talking about the incident in her bedroom when she was 15, she said: "He reached my bedroom and I was by the door. He gave me another one of his big hugs and tickles and my heart was booming."
She said Harris then put his hand down her trousers.
"When he got downstairs, he just started laughing and joking with everybody," she added.
The woman said she finally decided to go to the police in 2012 after seeing Harris take part in the Queen's Diamond Jubilee celebrations.
"The TV was on and Rolf was on the box, and I just thought: 'Cant I get away from this bloody man?'
"He's been on the telly quite a lot recently and it's like he invades my home," she said.
"That's when I decided I wasn't going to have any more of it," she added.
The court has previously heard that the entertainer, known to millions in Britain and Australia for his work as a TV presenter and a string of pop-music hits, was a Jekyll and Hyde figure who gained the trust of children before abusing them.
After being confronted by a letter from his alleged victim's father, Harris replied with a confession in which he accepted that he had had a sexual relationship with the woman but did not say it had occurred while she was under-age.
"When I see the misery I have caused ... I am sickened by myself," the jury heard he wrote in the letter.
"We can't go back and change things we have done in this life. I wish to God I could."
The trial continues.