It's exempt from the calculation of the estate's value for inheritance tax, hence tax-free, provided it was not ' a gift with reservation'. that is provided that neither of your parents retained any interest in it by living in it or using it as a second home or doing anything else to suggest that the gift was not an absolute surrendering of every right to any benefit from it.
If you are thinking of capital gains tax,there'll be something to pay on sale unless the property was your 'principal residence'. (If you own two or more residences you have to declare one of them as principal residence. The Revenue don't care which. It could even be a house you never lived in but they won't be keen to accept a property which is clearly let as an investment property throughout !)