declaration of spanish apartment query

A relative of mine bought an apartment in spain several years ago. he is now about to dispose of the apartment (at a loss). the owner has never declared to the Irish revenue that he owns the apartment.
Q1: Should the apartment have been declared on the annual tax return or in some other means to the irish revenue?

Q2: the fact that the asset is being disposed of at a loss. is there any tax benefit that the seller can claim on a loss?

The acquisition of capital assets should be put on a Form 11, were they in receipt of any income from the property.

Capital losses can be offset against gains.

thanks joe 90.
it was never rented. would they need to fill out a form 11 considering there was no income?

"Capital losses can be offset against gains." do you mean if they sold another asset for gain they could offset the CGT on that sale?