In the first act of La Forza Del Destino, Leonora spends time with her lover, Alvaro, when her disapproving father, the Marquis of Calatrava, surprises them. A fight ensues, but Alvaro decides to act honorably and drop his gun in surrender. But the force of destiny is strong - the gun goes off and kills the Marquis.
Click here to listen to the recording, which stars the inimitable Placido Domingo and Leontyne Price.
You can read more about the opera here.