Express surprise after learning something new. Only used with '이다' and '아니다' (sometimes in combination with '-으시'), and is stronger than 군(요)/구나 in these special cases.
Examples
그 남자 <span class='focus'>말이로군요</span>.
Ah, you're talking about that man. (That's who you're talking about)
그래서 기분이 안 좋은 <span class='focus'>거로구나</span>.
I see -- so that's why you're not in a good mood.
그건 그냥 마음이 변했기 때문... 아니, 그게 <span class='focus'>아니로군요</span>.
That's simply because she changed her mind... no, wait, that's not it.