annulment
Annulment is the declaration that a marriage has had no legal existence, as opposed to a divorce, in which it is understood that a marriage has simply failed. Annulment erases a marriage; divorce simply ends it.
The most famous annulment in European history is probably that sought by Henry VIII from his first wife, so that he might marry his mistress. The papal refusal to grant the annulment caused the king to break off from the Roman church.