Marriage and murder

Catherine is a member of the Vrazei, an underground group dedicated to helping the kingdom fight against the Rohakiloe. The Rohakiloe are inhumanely strong, fast, and violent. Worst of all they're nearly indistinguishable from humans. Left unchecked they'd kill everyone and destroy the kingdom. One of these Rohakiloe has replaced the prince, and Catherine was forced to get close to the imposter to assassinate him, so close that they end up married. Doesn't count if he's dead, right?