If you're trying to figure out whether 'The Dark Prince' is suitable for a teen, here's how I look at it: there isn't a single universal rating because multiple books share that title. For example, the paranormal romance 'The Dark Prince' by Christine Feehan is firmly adult — think explicit sexual content, mature themes and scenes that are usually recommended for readers 18+. On the other hand, if you're talking about a dark fantasy or YA retelling with a similar title, the recommended age can swing down into the mid-teens depending on violence and language.
Personally, when I vet a book for younger readers I check a few quick things: the publisher's age label, reader reviews on places like Goodreads, a search for content warnings (sex, graphic violence, self-harm), and a sample chapter. If those red flags pop up, I treat it as adult material. If the themes are dark but handled with restraint, it might be OK for 15–17-year-olds with parental guidance. Bottom line: find the specific author/edition, skim the first chapters, and decide based on explicit content rather than the title alone — that's saved me from awkward surprises more than once.