CGT On House Sale

I realize that the question about CGT if not your residence has been answered before, but I have a specific circumstance.

I bought a house in 1999 for around 130,000 Euro. It is now worth €400,000. CGT looks like it will be very high if I sell now.
In the meantime...... I left the country in November 2000 and my brother lived in it up until now. I never "officially" rented the house. I am moving back to a different part of Ireland now and would like to sell the house to buy another one closer to my work.

Am I liable for CGT given the house has not been rented even though I was not resident in the country?
If I do move back into the house and want to sell it in the future, will I always be liable for CGT for the years I was not there?

I never "officially" rented the house.

Can you explain what you mean here? I don't understand the use of the word "officially" and the surrounding quotes. I can only assume that you mean that your brother actually paid you rent - or paid your mortgage on your behalf from his own means, which is the same thing - but that you never ?

Where a house is rented out (other than under the owner occupier ) then a proportion of any eventual resale gain is subject to CGT. Basically if you own the property for x years, live in it as your PPR for y years and rent it out for z years then (((z-1) / x) * 100) is the percentage of any resale gain assessable for CGT.

Where a property originally bought as an owner occupied property is subsequently rented out (other than under the rent a room scheme) within five years of purchase (as may apply here) then a also applies.

To answer "Officially".
My brother paid a contribution to the mortgage, below the mortgage value, although I did not declare it.
Is there any concession with renting when it is a family member?
If the house was not rented and I was not resident in the state, would it still be liable for CGT?

But the house was rented. If you are seeking advice on how to evade tax, you came to the wrong place.

Is there any concession with renting when it is a family member?

As far as I know Revenue do make some allowance for somebody (e.g. a family member) to live in a property on a householder's behalf in such a way that it allows the property owner to retain his/her PPR/owner occupier status. There is also an allowance for retaining this status when one is seconded to work abroad (as opposed to willingly deciding to emigrate). However I do no know the ins and outs of these and whether or not they are relevant to this situation. However I suspect that they are not and that, as mentioned previously, you have effectively rented the property even if you have not declared this.