Grammar
-군요
new realization
Form
Verb/adjective stem + -군요; noun + -(이)군요 — “oh, I see!”.
Function
Marks a new realization or an explanation just understood, often on hearing information.
Why this form?
-네요 — “oh, it is…”: often a direct discovery; -군요 can focus more on understanding the information.
Forms not to confuse
-네요
정말 춥네요. — Oh, it is really cold.
Examples
그래서 그 소리였군요! — Oh, so that was the noise!
아, 그런 이유였군요. — Oh, so that was the reason.