The Lost Prince - a lost book

I encountered this book in the school library (I think) as a child. I had no memory of who wrote it -- I never took any notice of authors -- nor of the title, and had never seen another copy, but when I encountered a plot summary in a list of 'Ruritanian romances' I recognised the characters at once.
Although I still think I was mixing it with another lost novel I read around the same period ,in which the protagonist was a refugee child sent to America post WWII whose real identity was that of the heir to a small Balkan kingdom whose father had been execrated as a Nazi collaborator; his name was Michael, and thus "Michael, Prince of <wherever>" becomes plain "Michael Prince" in his new life...

The Lost Prince, by Frances Hodgson Burnett