AIB sold its shareholding in a Bulgarian bank -- which it bought for €216m -- for a mere €100,000, the lender has been forced to admit.
It means the bank offloaded its 49.99pc in Bulgarian- American Credit Bank (BACB) for only a tiny fraction of what it paid in 2008.
AIB, which is 93pc owned by the State, said it already booked the losses from the investment.
The value of its stake was written down to zero over several years and finally written off completely in 2010, the bank said.
It confirmed the purchase price of €100,000 reported in Bulgaria was accurate, but added that it would not affect this year's accounts.
AIB said in May it had agreed to sell the stake but did not disclose the price paid.
A statement on BACB's website said the stake had been bought by Clever Synergies Investment Fund, which is owned by businesswoman Tsvetelina Borislavova.
BACB is a publicly listed bank based in Sofia in Bulgaria, and is focused on small to medium-sized enterprises.
According to reports in Bulgaria, the buyer is also likely to take on BACB's outstanding debt.
Ms Borislavova is a former minority shareholder in CIBank, the Bulgarian subsidiary of the Belgian banking group, KBC.
An AIB spokeswoman said, as a result of the sale, it would no longer have to fund the Bulgarian lender.