だとは知らなかった

I didn't know that ... was ...; I had no idea that ...

→ だ

phrase Uncommon #15,602

I didn't know that ... was ...; I had no idea that ... Used to express surprise upon learning information. The pattern だとは知らなかった follows a noun or な-adjective and emphasizes that the speaker was unaware of the fact. It is generally neutral in politeness, while よ or other sentence-ending particles can make it more conversational.

JA: トムがダンスの先生だとは知らなかったよ。

EN: I had no idea Tom was a dance teacher.

トムがダンスの先生だとは知らなかったよ。

I didn't know Tom was a dance teacher.

私は彼が日本人だとは知らなかった。

I didn't know he was Japanese.

君がそんなに野心的だとは知らなかった。

I didn't know you were so ambitious.

— 教皇選挙 (2024)

トムはその赤ん坊がメアリーだとは知らなかった。

Tom didn't know that the baby was Mary.

今まで兄弟だとは知らなかった。