Morganatic

is read as \mawr-ga-NAT-ik\ and means a marriage between one of royal or noble birth (mostly man) and one of lower rank (usually woman) in which the lower ranker or their children (if any) has no claim to all the possessions of the higher ranker.

Morganatic marriages are not common anymore these days though in some marriages between the rich and the poor, there is what we call pre-nuptial agreement. Senator Francis Pangilinan and Mega Star Sharon Cuneta (both from affluent families) signed a pre-nuptial agreement before they got married.

dictionary.com page link for morganatic