The False Prince by Jennifer A. Nielsen
When Sage is unexpectedly plucked from his orphanage by an alleged nobleman patriot, he is forced into a life or death competition along with three other boys. The winner will be tasked with impersonating the king's long-missing son in an effort to avoid a civil war. Sage's confidence is matched only by his reluctance to live a life a deceit.
This is an extraordinary adventure filled with danger and action, lies and deadly truths... all of which will have readers clinging to the edge of their seats!