The False Prince (Scholastic Press, 2012) by Jennifer A. Nielsen has it all: orphans, plots, a lost prince, danger and adventure. Sage, one of the orphans forced to learn how to impersonate the lost prince, begins his story with, "If I had to do it all over again, I would not have chosen this life. Then again, I'm not sure I ever had a choice."
I found the book hard to put down and am thrilled to find out it is the first in a trilogy. The next book is The Runaway King and the third is The Shadow Throne. In February 2015, there's supposed to be news on whether or not Paramount will make a movie of The False Prince. I hope it is a yes!
In addition, Author Jennifer A. Nielsen has two series already out and another one where the first book, The Mark of the Thief, is coming in February 2015. Read about her and her books on her website.