morganatic
adjective
mor·ga·nat·ic ˌmȯr-gə-ˈna-tik 
: of, relating to, or being a marriage between a member of a royal or noble family and a person of inferior rank in which the rank of the inferior partner remains unchanged and the children of the marriage do not succeed to the titles, fiefs, or entailed property of the parent of higher rank
morganatically
ˌmȯr-gə-ˈna-ti-k(ə-)lē
adverb 
Did you know?
Although the deprivations imposed on the lower-ranking spouse by a morganatic marriage may seem like a royal pain in the neck, the word morganatic actually comes from a word for a marriage benefit. The New Latin term morganatica means "morning gift" and refers to a gift that a new husband traditionally gave to his bride on the morning after the marriage. So why was the New Latin phrase matrimonium ad morganaticam, which means literally "marriage with morning gift," the term for a morganatic marriage? Because it was just that - the wife got the morning gift, but that's all she was entitled to of her husband's possessions.
Word History
Etymology
New Latin matrimonium ad morganaticam, literally, marriage with morning gift
First Known Use
1728, in the meaning defined above