ことに気づかなかった

didn't notice that

→ こと
phrase Rare #44,120
didn't notice that Follows a clause to say that someone failed to notice or become aware of what happened.
JA: 彼が帰ってきたことに気づかなかった。
EN: I didn't notice that he had come home.

トムはメアリーが出発したことに気づかなかった。

Tom didn't notice that Mary had left.

昨日の夜、彼女がチキンを食べていたことに気づかなかった?

Didn't you notice that she was eating chicken last night?

— バジュランギおじさんと、小さな迷子 (2015)

私は彼が居たことに気づかなかった。

I didn't realize he was there.