Don't worry...two things:
- You're likely to be non Irish domiciled and therefore only subject to Irish CGT on foreign gains to the extent that those gains are brought into Ireland. That's probably what that advisor was referring to.
- In any event if you pay 33% CGT in South Africa, there's a Tax Treaty between Ireland and South Africa which eliminates double taxation so you'd get credit for the South African CGT against your Irish CGT liability. Assuming that gains are calculated similarly in both jurisdictions (which should be the case), you'd have no further tax to pay in Ireland. So my first bullet point may be largely irrelevant.