If an executor or next-of-kin of the deceased, who has not been personally served with a citation or who has not had notice thereof in time to appear pursuant thereto, establishes to the satisfaction of the High Court a claim to probate of will or to letters of administration in preference to the Administrator-General, any letters of administration granted in accordance with the provisions of this Act to the Administrator-General--
         (a) shall be revoked, if a will of the deceased is proved in the State;
         (b) may be revoked, in other cases, if an application for that purpose is made within six months after the grant to the Administrator-General and the High Court is satisfied that there has been no unreasonable delay in making the application, or in transmitting the authority under which the application is made;
     and probate or letters of administration may be granted to such executor or next-of-kin, as the case may be.