-군요/는군요 is used to express surprise or wonder upon learning something new either by direct observation or experience or by hearing about it from someone else.

It corresponds to 'I see (that)', 'indeed', 'how', or simply an exclamation point (!) in English.

For adjectives, -군요 is added to the stem, while for verbs, -는군요 is added.

This expression can also attach to nouns by adding -(이)군요. To express the past tense, it is added to the past tense ending to form -았/었군요.'

Details

In the informal plain style, -군요 changes to -구나/-군 in the case of adjectives, -는구나/-는군 in the case of verbs, and -(이)구나/(이)군 in the case of nouns.

A: 저 아이가 제 동생이에요.

That boy/girl is my little brother/sister.

B: (혼잣말로) 아. 저 아이가 동생이구나.

(To oneself) Oh, so that's his/her little brother/sister.

A: 엄마, 오늘 학교에서 일이 있어서 늦게 왔어요.

Mom, today I was busy at school, and that's why I'm late.

B: 응. 그래서 늦었구나.

Okay, so (I see) that's why you're late.

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Express surprise after learning something new.

Details

Usage

Tense	Word type	Pattern
Present	Action verb	는군(요) or 는구나
Present	Descriptive verb	군(요) or 구나
Past	Verb	았/었군(요) or 았/었구나

For usage with noun, 이다 is used to make the transition.

A/V-군요/는군요

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Usage