Morganatic marriage

A morganatic marriage is a marriage between a royal person and a person of lower rank. The royal person's title titles and privileges do not go to the spouse or to any children, who do not become heirs. However, the marriage is considered legitimate, and the children are not bastards.
A morganatic marriages is now rare and is sometimes called a left-handed marriage because in the wedding ceremony, the groom usually held his bride's right hand with his left hand.
Most famously, Archduke Franz Ferdinand had to get a morganatic marriage so that he could marry Sophie, Duchess of Hohenberg, because she was a noble of a lower rank.