4.—(1) For the purpose of determining the person or persons who would in accordance with rules of court be entitled to a grant of probate or administration in respect of the estate of a deceased person, the deceased shall be presumed, unless the contrary is shown, not to have been survived—
(a)by any person related to him whose father and mother were not married to each other at the time of his birth; or
(b)by any person whose relationship with him is deduced through such a person as is mentioned in head (a).
(2) This paragraph does not apply in relation to the estate of a person dying before the commencement of this paragraph.