Back at Disney Castle, we get a look around a really wonky library as we see the text of the King’s letter overlayed across the scene. It confirms what you imagined: “the King” is the icon himself, Mickey Mouse, and is (somewhat comically) written to reflect his inflection. But strangely enough, you don’t hear the Mouse’ s legendary voice, even though the scene is shot as though there was supposed to be a voiceover. The reason for this, purportedly, has to do with Disney’s fears of letting Square handle their crown jewel in this first outing, so he was pushed back as much as possible. Rest assured that when he is voiced, he’s voiced by the legendary Wayne Allwine, who voiced the role from 1977 to his death in 2009.
The scene tells us a lot about the plot, and also the arrangements at Disney castle. Mickey writes that he’s noticed several stars going out. A pretty dire, apocalyptic start to our story. As a result, he’s gone off without any warning to investigate. Thankfully, he seems to have a hunch on what to do, and instructs Donald to find Goofy and locate someone with “a ‘key'” that will help them out of this, and to stick with the key no matter what. Mickey also tells Donald to inform Minnie even though Donald was clearly trying to hide this from Minnie in the last scene. If it’s been a while since you watched a Donald Duck cartoon: Donald’s an asshole.