In Die Walküre, the second of Richard Wagner's four-opera cycle Der Ring des Nibelungen, Siegmund and Sieglinde, the twin children of the God Wotan by a human woman are separated as children. Years later Siegmund, seeking refuge during a storm comes to the home of Sieglinde who is now married to a brute Hunding. They do not recognize each other and are attracted to each other. After Siegmund draws the sword plunged into an ash tree that no one had been able to remove, they realize that they are brother and sister and are in love. They spend the night together and Sieglinde becomes pregnant with a child that will one day become the hero Siegfried, the hero of the next opera in the cycle, whose title bears his name.
Another example of incest is the relationship of Siegfried and Brünnhilde, since Brünnhilde is Wotan's daughter (by Erde) and thus Siegfried's aunt by blood. As Performer/Anna Russell pointed out.