(1) The appointment of a reversionary heir becomes ineffective at the end of a period of 30 years after the devolution of the inheritance, if the circumstances giving rise to reversionary succession do not occur before this time. It remains effective even after this time
1. if reversionary succession is directed for the case in which a particular event occurs relating to the person of the provisional heir or of the reversionary heir and the person in relation to whose person the event is to occur is alive at the time of the devolution of the inheritance,
2. if it is provided that, if a brother or a sister is born to the provisional heir or to a reversionary heir, the brother or the sister is the reversionary heir.
(2) If the provisional heir or the reversionary heir in relation to whose person the event is to occur is a legal person, the thirty-year period applies.