I know it is not good to study grammar from songs. However, I am curious if this structure below is some kind of grammar.
7년을 만났죠 아무도 우리가 이렇게 쉽게 이별 할 줄은 몰랐죠
I know the structure "ㄹ 줄 모르다" but in this sentence why there is 은 here? Hope someone can explain it. Thanks.
Link for the song lyric: 7년간의 사랑