Lost Orphaned Royalty

This is when a child, raised as an orphan, turns out to actually be the next heir to the throne, or similarly destined for a position of authority or political power. There are a multitude of plots that could stem from this trope: The parents could have sent him away so he could have a "normal" childhood, the orphan could be well aware of his royal status, but just needs a way to get it back. The orphan could suddenly be thrusted into the big chair that is the monarch. So there are a lot of possibilities when it comes to orphan monarchs. If the villain is all like, "I will kill the king and his descendants so I can take the throne." Then the orphan can be on the run from the villain trying to kill him... Or he could be the overlooked heir that the villain didn't realize was a rightful heir to the throne. The orphan could BE the villain, obsessed with getting the life he deserves to have, being the true heir and all...

Suddenly-Suitable Suitor is a common plot twist.

Compare Moses in the Bulrushes, Changeling Fantasy and Switched at Birth.

Film

 * Lone Starr of Spaceballs

Literature

 * Shasta, from CS Lewis's The Horse and His Boy is one.