Prince Harry was regarded as a "weak" student at Eton and needed to be helped, his former art teacher has claimed at an employment tribunal.
Ms Forsyth lost her job in the summer of 2003
Sarah Forsyth, whose contract ended in 2003, said parts of a painting featured in newspapers as the Prince's A-level work were completed by another teacher.
And Ms Forsyth, 30, said help she gave Harry for AS-level work was "unethical and probably constituted cheating".
She denies her job loss was due to her teaching and claims unfair dismissal.
In cross-examination at the Reading hearing, Ms Forsyth said she believed "reasons other than the teaching" including the "Prince Harry mess" lay behind her dismissal.
In a statement, Ms Forsyth also alleged she secretly recorded Harry thanking her for the help when it became clear she would not get her job back.
"I have recently seen for the first time extracts of the written material which was submitted on Prince Harry's behalf and can confirm that it was nearly all written by me," she added.
The prince's former teacher said she assumed she had been asked to help him because he was "a weak student" and went on to claim that a colleague who marked Harry's entrance exam had been "desperate" to award marks to help him pass.
Miss Forsyth has also alleged that Ian Burke, her former head of department, would occasionally paint for the boys while he talked to them about betting or football.
Pupils encouraged this behaviour, she said, by keeping the teacher on his "pet subjects".
In her statement she said Mr Burke worked on the boys' paintings in their absence, including Prince Harry's work which later featured in newspapers.
Mr Burke said, in a supplementary statement to the tribunal, that his former colleague's claims were "a misinterpretation of a friendly atmosphere" and said claims that he had finished pupils' work were "completely untrue".
Prince Harry is beginning officer training at Sandhurst Military Academy in Surrey this week.
The Royal Family has denied any cheating by Harry took place.
Ms Forsyth worked at Eton until the summer of 2003, when her contract was not renewed.
The school maintains that she did not sit alone at a computer and write out the text to the AS project, as she has claimed.
It has said that three separate teachers saw her sitting with Harry working on his coursework journal.
Eton has previously said Ms Forsyth's tape is inaudible in parts and, in any event, the whole issue is irrelevant to the dismissal.