You have a liability for Capital Acquisitions Tax.
You are getting a gift from your aunt of €90,000 - the difference between the price you pay and the value of the property.
Over your lifetime, you are allowed up to €40,000 tax free from your aunts and uncles.
So if you have not received any other gifts, you would be liable for Capital Acquisitions Tax of 33% of the excess over €40,000 or €50,000 @ 33% = €16,500
However, as the Capital Gains Tax and Capital Acquisitions Tax arise from the same event, the gift of the house, you will get a credit for the CGT paid by your aunt.
So you will not have any liability.