건 아니겠죠

it isn’t that …, is it?

→ 것+은
phrase Rare #20,900
it isn’t that …, is it? Used to seek reassurance or confirmation, often with the hope that the answer is no. The omitted part comes before 건.
KO: 네가 그걸 잊은 건 아니겠죠?
EN: You didn’t forget it, did you?

근데 섹스 랑 관련 있는 건 아니겠죠?

But it’s not related to sex, is it?

— 토니 에드만 (2016)

흉터가 남는 건 아니겠죠?

It won't leave a scar, will it?

— 걸리 보이 (2019)

잠깐만요 이름을 말한 건 아니겠죠?

Wait, you didn't say your name, did you?

— 저수지의 개들 (1992)