depends on the situations. I will say another different meaning from previous answer. 이럴줄은 몰랐어: 이런 식의 결과가 나오게 되리라고는 예상하지 못했어. I didnt expect(예상하지 못했어-몰랐어) this kind(이런식의) of result(결과가) would came out.(나오게 되리라고는)

이럴줄은 몰랐어 is a short form of 이렇게 할 줄은 몰랐어 이렇게(in this way)+할(do)+줄(method,way)+은(subjective particle)+몰랐어(past of don't know) I didn't know you did it in this way.