morganaticadjective
/ˌmɔː.ɡəˈnæt.ɪk //ˌmɔːr.ɡəˈnæt̬-/A morganatic marriage is one in which one partner is of higher social rank, and the other cannot claim this partner's title or possessions or pass them to their children:
a morganatic marriage/union
the Archduke Franz Ferdinand's morganatic wife, Sophie Chotek