The Commercial Court has ordered four businessmen to repay a €6.3m loan from AIB to develop land in Co Meath.
The four men, including Jim Mansfield junior, had contested the bank's application for immediate repayment.
The action was taken by AIB against James Mansfield Jr, Palmerstown House, Johnstown, Co Kildare, Brian Higgins, Allensgrove, Celbridge Road, Leixlip, Co Kildare, Glen O'Callaghan, Drapier Road, Dublin and Seamus Kavanagh, Kyle, Killea, Templemore, Co Tipperary.
They claimed the loan was not a commercial transaction and that they were entitled to be treated as consumers and the case should go to a full hearing.
Mr Mansfield Jr had also claimed he was not an equal partner with the other three men and had not fully understood the nature of the loan because he has a reading age of seven.
The court heard that he is a director of 25 companies and can fly a helicopter, although could not obtain a licence to do this because it requires a written test.
Mr Justice Peter Kelly said a report handed into court from an educational psychologist said Mr Mansfield Jr could read only very basic sentences such as 'the cat sat on the rug'.
Mr Justice Kelly said Mr Mansfield Jr had a wide range of business interests, but had submitted to the court that these were family businesses and he was guided and advised by family members.
The judge noted that his signature appeared on the annual returns of these businesses.
He said it was clear he had a good deal of experience of commercial and financial matters, however despite this curious situation he would have to accept that he had a disability with a reading age of seven.
However, the judge said he was not entitled to claim he was unaware of what he was signing and had not made out an arguable defence in that regard.
A previous hearing was told that the four men had borrowed the money in 2003 to buy land and develop apartments at Duleek Co Meath.
AIB had demanded repayment of the loan last September.
