Highest-grossing movies you didn’t know were books

From "Harry Potter" and "Twilight" to "The Lord of the Rings" and "The Hunger Games," it's no secret that some of the highest-grossing movies were best-selling books before they hit the big screen.

But for every obvious adaptation movie like "Peter Pan" or "The Great Gatsby," there are book-to-movie adaptations that strike Hollywood gold with many fans never even realizing that they appeared in bookstores before they hit the movie theater.

So, consider yourself a book and movie whiz? Click through to find out which films were actually books before they became box office winners:

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