なんて、知らなかった

I didn't know that...

→ なんて
phrase Rare #36,214
I didn't know that... Expresses surprise upon learning something. なんて adds emphasis or conveys that the information was unexpected; the phrase is often followed by わ, な, or よ.
JA: 君が料理もできるなんて、知らなかった。
EN: I didn't know you could cook, too.

病気だったなんて、知らなかった

I had no idea you were sick.

彼氏がいるなんて、知らなかった

I had no idea you had a boyfriend.

トムがまだここで働いてるなんて、知らなかった

I didn't know Tom still worked here.