Lohengrin (opera)
Count Telramund explains that the Duke of Brabant had recently died.  As he lay dying, he had asked Telramund to look after his daughter Elsa and his son Gottfried.  One day the two children had gone into the forest and Elsa had returned alone.  The Duke tried to find out what had happened to Gottfried.  The Duke’s wife Ortrud persuades the Duke to accuse Elsa of murdering her brother.  The duke then makes himself the king of Brabant.