x1 is morganatic in property x2 according to rule/law/custom/culture x3.
x1 may be an event (such as "state of marriage" or "wedding"), a relationship (such as that between a child and their parent), etc. A marriage or a relationship between parent and child which is morganatic is recognized, official, legitimate, and subject to customs or rules which apply to non-morganatic such relationships (such as prohibitions against adultery) in the given culture, but at least one party in the relationship is not entitled to the titles, rights, property, etc. of the other(s) by relation or inheritance. The exact details depend on x3 and the type of thing which x1 is.