nēmō est hērēs vīventis

Meaning

1. New Latin“No one is heir of a living person”: the inheritance of an estate is decided only upon the death of its owner, and nobody is “heir” while that person is alive (only heir apparent or heir presumptive).
   Suum enim nasci dicimus, qui post mortem nascitur: quoniam sicut viuentis nemo est haeres, ita nemo testatori viuo suus haeres nascitur.Indeed, we say that his [heir] is born, when [the heir] is born after his death: for just as no one is heir of a living person, so no one is born heir to a living testator.1595, Joachim Mynsinger von Frundeck (citing Mario Salamoni degli Alberteschi), Apotelesma, sive Corpus Perfectum Scoliorum, ad Quatuor Libros Institutionum Iuris Ciuilis, page 285:

Origins

Of uncertain specific origin; current as a maxim across Western Europe by the 16th–17th centuries, in both England and the Continent. Later treated as a precept of common law, though its occasional ascription to the 13th-century English jurist Bracton is spurious.