The idea of using a prologue in your sequel to a series of fiction books with long established lore that you are publishing years later isn't a bad one. It's a great way to recap the story for old readers and make the backstory accessible to new readers without having one or more chapters that waxes poetic about all the stuff that happened before.

It'd be a nice touch if Murtagh could go five seconds without reminiscing or wangsting about something that happened in the series. As it, it's kind of wasted.