"This book was about some boys being taught to impersonate the lost crown prince"

[conuly]

"I remember there was some sort of crazy twist at the end!!!!"

Me: You are charmingly naive. The protagonist actually being the lost crown prince is not a crazy twist, even if you've never seen it before in print somehow. You know what would be a crazy twist? If somebody whose grand plan depended on being accepted as heir was actually a really good con artist, and maybe had enough inside information to fool those in the know.