must have been; there probably was; probably had
무슨일이 있었을 거 야
Something must have happened.
그녀는 발작이 있었을 거 야
She must have had a seizure.
— 아바타: 물의 길 (2022)
시카고 면 실라르드와 페르미 밑에 있었을 거 야
If it had been Chicago, I would have been working under Szilard and Fermi.
— 오펜하이머 (2023)
무슨 사정이 있었을 거 야
There must have been some reason.
— 중앙역 (1998)