Property in Derry, but Resident in Donegal. Income Tax.

[Becca]

If someone is permanently resident in Co.Donegal, but purchases an investment property in Derry, would they pay UK income tax, or Irish income tax, or some combination on the investment property...?

And any tax relief on investment property, would this be according to Irish tax rules/relief, or UK rules/relief?

Thanks for any help..!