Prince Harry's art teacher taped him admitting he had done little work on a coursework piece counting towards his A-level, an employment tribunal heard.
Miss Forsyth is claiming unfair dismissal from Eton
Sarah Forsyth wanted to prove she had been asked to work on his project at Eton College, the tribunal was told.
On her transcript Harry allegedly said of the AS-Level piece "..tiny, tiny bit...I did about a sentence of it".
But Eton says the tape is inaudible in parts and the whole issue is irrelevant to the unfair dismissal case.
The Royal Family has strenuously denied there was any cheating.
Miss Forsyth's QC Robin Allen said she was asked to "carry out certain work on the project of Prince Harry" after she was told she would not get a permanent job, but instead be put on a one-year contract.
Prince Harry got a B for his art A-level
Miss Forsyth says it was one example of harassment by Eton's head of art Ian Burke, about whom she had made other complaints which were ignored.
"She was not happy about it. She feared that if she complained about it at the time she would be victimised," Mr Allen told the tribunal.
Miss Forsyth's contract was terminated at Eton on 16 June 2003.
But one month before, aware of her "precarious position", she took the prince into her office minutes before he was due to sit his A-Level painting exam.
'Pretty grubby' conduct
Mr Allen said it was a last resort to prove Mr Burke's "cheating" after previous allegations against him had not been acted upon.
"That is why she felt it necessary to record an admission by Prince Harry that the work he had done for his expressive project was largely hers," he told the tribunal.
But Nigel Giffin QC, for Eton College, said the "Harry issue" had no relevance to the case and should be excluded from the evidence.
And he accused Miss Forsyth of "pretty grubby" conduct, saying it was an attempt by her to secure a larger pay-off than the £10,000 she was offered.
The college's own transcript of the tape is different to Miss Forsyth's and the Royal Family say it has been edited and it is difficult to make out what the prince is talking about.
Eton says making the tape was a gross breach of trust between pupil and teacher and say it is "far fetched" to describe it as a piece of evidence.
The tribunal continues.