I remember once I have seen 「なの」 was not placed at the end of a sentence (meaning it was not a question) ever since then I wondered what it meant but didn't have any clear examples. Today I saw this sentence in my textbook:
The textbook translates this sentence as "It is a boy, I know". The topic of the chapter is not about the 「なの」 part, so no explanation is given about it.
What does 「なの」 mean here?
Edit 1: Got the comma right in the translation. Sorry for misunderstanding!