"A prince is the son of a king." The word "prince" there should not be capitalized, since it's not used as part of someone's title. "The person who will inherit the throne of England is Prince Charles." Here, "Prince" is capitalized because "Prince Charles" is someone's title, and as such, a proper noun. "The song 'Purple Rain' was written by Prince." Here, "Prince" is capitalized because it's someone's name. Here are the cases about which I'm uncertain: Case 1: "Hey, there you are, Prince Ralph. What can I get for you, Prince?" Case 2: "Hey, there you are, Prince Ralph. What can I get for you, my Prince?" In each sentence, the latter of the two instances of "prince" do not use the full title, but they are used to directly address the prince. Should they be capitalized? My first instinct is to lowercase both of them, but I'm looking for additional opinions. Edit: The context is a work of fantasy fiction with the prince as the main character. The full formality that would hold in real world England, for example, need not apply.