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Phrase(s): Who would have thought? [and] Who could have thought?
a question phrase indicating surprise or amazement; I would never have guessed that something so surprising could happen. (No answer is expected.) • Tom: Fred just quit his job and went to Africa. Bill: Who would have thought he could do such a thing? • Andy: They say Bill is training for the Olympics in his spare time. Rachel: Who would have thought?
McGrawhill's American Idioms And Phrasal Verbs