User blog comment:Megadracosaurus/The Antagonist Of HTTYD3/@comment-7628730-20140918182627/@comment-24018437-20140918202741

I undertstand what you mean, but it isn't necarily true. Take Rise of the Guardians for example. DreamWorks made a movie of it, even though the Book series wasn't finished yet. And despite sharping the same endings, you have to Remember that the books and films are still completely differant. So realy, it wouldn't matter which one would came out first. And HTTYD3 is planned for 20017, btw. Cressida Cowell usually takes one or two years to write, so its safe to assume the Book Will come out before the film. 'Sides, I once read a post of Cressida Cowell on a website (Forget which one) that the last Book would be finished next year or so, or slightly later, becuae She has problems with her eyes.

And no, it wouldn't neccarly ruin it. Look at the Harry Potter example. Most people already knew the ending, because they read the books. But did that stop from seeing the movies?