26 C.F.R. § 513.10
A nonresident alien who is resident in Ireland for the purposes of Irish tax and who is a beneficiary of a domestic estate or trust shall be entitled to the exemption from, or reduction in the rate of, United States tax provided in Articles VI, VII, VIII, IX, and XV of the convention with respect to dividends, interest, royalties, natural resource royalties, and real property rentals to the extent such item or items are included in his share of the distributed or distributable income of such estate or trust. In order to be entitled in such instance to the exemption from, or reduction in the rate of, tax such beneficiary must otherwise satisfy the requirements of these respective Articles of the convention and must, where applicable, execute and submit to the fiduciary of such estate or trust in the United States the appropriate letter of notification prescribed in §§ 513.3(b) , 513.4 , and 513.5 .
26 C.F.R. §513.10