The jury at Southwark Crown Court heard how Rolf Harris was a "dirty old man" who assaulted a child at a community centre near Portsmouth at one point between 1968 and 1970.
The woman, speaking behind a screen, said initially she was confused and thought there must have been some kind of mistake:
It was very quick. In fact so quick that I thought, 'what's happened?'. The first time I thought, no, not deliberate. I thought, 'what's going on?', because there were a lot of people around and I didn't process what had happened.
She went on to describe how he repeated the assault, "more aggressively", and broke down as she said she "wasn't the same child" afterwards.
She said Harris had performed Two Little Boys at the event. Harris denies all 12 counts of indecent assault on four alleged victims.
It didn't matter if it was going to hurt me or not. It felt very agressive and I knew that it wasn't an accident.
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The child died on her injuries and another 14-year-old girl was injured after the buggy they were travelling in was involved in a car crash.
Cloud thickening from the west throughout the day. Rain in northwest later.
The Songs of Praise presenter has voluntarily agreed not to appear on BBC whilst an investigation takes place.