(으)ㄴ 줄 모르다 [Intermediate Grammar]

 - (으)ㄴ 줄 모르다

→ If an incomplete noun of a situation or an intention is used after a modifier of a verb or an adjective '-(으)ㄴ/는/(으)ㄹ', it indicates that I understand it at the present time but didn't figure out the situation in the past. Usually the verb '몰랐다' or '생각 못했다' is used after it.

Example: 

1. 회사 규칙이 이렇게 까다로운 줄 몰랐어요.
I didn't know the company's rules were so complicated.

2. 전화번호가 바뀐 줄 모르고 제가 실수했습니다.
I didn't know the number was changed, so I made a mistake.

3. 제가 쌍둥이를 낳을 줄 생각도 못했어요.

 I didn't know I gave birth to twins.

4.제 남동생이 이렇게 노래를 잘하는 줄 몰랐어요.

I didn't know my younger brother could sing so well.

5.한국인 줄 모르고 영어로 말했습니다.

I did not know Korean and spoke English.