“executor” means any person to whom letters of administration have been granted by a Master or an Assistant Master of the High Court appointed under the Administration of Estates Act, 1965 (Act No. 66 of 1965), in respect of the estate of a deceased person under any law relating to the administration of estates, and includes a person acting or authorized to act under letters of administration granted outside the Republic but signed and sealed by such a Master or Assistant Master for use within the Republic and, in any case where the estate is not required to be administered under the supervision of such a Master or Assistant Master, the person administering the estate;