a petty or insignificant prince who rules some unimportant principality
<noun.person>
a young prince
<noun.person>
Princeling \Prince"ling\, n. A petty prince; a young prince.
And there is indeed much to be said for it despite a dopey libretto that bears passing resemblance to "The Student Prince" (except that Rossini's disguised is not some German princeling, but the ruler of half the world).