steepholm

I can't think of one that does precisely that, but Pushkin. and thus Mussorgsky's BORIS GODUNOV, has a guilty but essentially virtuous and repentant usurper and an true heir who actually isn't but has been conned into thinking he is, and is the tool of bad people.

And de Musset's LORENZACCIO becomes totally corrupted by the effort of living at the usurper's court.