Problems understanding なの in this sentence


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:

> 男の子 **なの** は知ってる

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!




You can break なの down into the formal noun の and the adnominal copula な (i.e.,
a form of だ which shows up before nouns).

**Your sentence:** Basically, the sentence （彼が）男の子だ is embedded into は知ってる by
turning it into a noun using の.

> （彼が）男の子だ  
>  ⇒［（彼が）男の子な］のは知ってる

**Alternatives:** You could also write it as

> 男の子であるのは知ってる  
>  "I know that he's a boy."

which is equivalent in meaning but slightly more formal/literary/whatever
because it uses である in place of な to represent the copula. Another option is

> 男の子（だ）ということは知ってる。  
>  "I'm aware of the fact that he's a boy."

which gets across the same point in a slightly more lengthy way.

If it was simply 男の子は知ってる that would either be read as "The boy knows" or "I
know the boy", because there is no copula.




You can break なの down into the formal noun の and the adnominal copula な (i.e.,
a form of だ which shows up before nouns).

**Your sentence:** Basically, the sentence （彼が）男の子だ is embedded into は知ってる by
turning it into a noun using の.

> （彼が）男の子だ  
>  ⇒［（彼が）男の子な］のは知ってる

**Alternatives:** You could also write it as

> 男の子であるのは知ってる  
>  "I know that he's a boy."

which is equivalent in meaning but slightly more formal/literary/whatever
because it uses である in place of な to represent the copula. Another option is

> 男の子（だ）ということは知ってる。  
>  "I'm aware of the fact that he's a boy."

which gets across the same point in a slightly more lengthy way.

If it was simply 男の子は知ってる that would either be read as "The boy knows" or "I
know the boy", because there is no copula.

