Hello everyone!

I've come across a sentence that I don't understand at all, well, I have always wanted to know this thing, but, never got a clear reply to it.
"Ariel, who was invisible to all eyes but to Prospero's" --> The sentence means that Ariel was invisible to all except to Prospero, doesn't it?
Is the sentence simplified or something? Could it come from "Ariel, who was invisible to all eyes but wasn't to Propero's"?

(It sounds weird!)
"But" isn't a linker here, is it? If it were, could we use another one? or, it only works with "but"?
Thanks in advance for your help!