Please read Alexey Sklyarenko's annotations on Pale Fire, Ada and other Nabokov works here.
At the end of his commentary to Shade's poem Kinbote (in VN’s novel Pale Fire, 1962, Shade’s mad commentator who imagines that he is Charles the Beloved, the last self-exiled king of Zembla) says that he may pander to the simple tastes of theatrical critics and cook up a stage play, an old-fashioned melodrama with three principals: a lunatic who intends to kill an imaginary king, another lunatic who imagines himself to be that king, and a distinguished old poet who stumbles