Monkey's uncle
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The term monkey's uncle, most notably seen in the idiom "(Well,) I'll be a monkey's uncle", is used to express complete surprise, amazement or disbelief.[1] It can also be used to acknowledge the impossibility of a situation, in the same way that "pigs might fly" is used. An example is if one says: "I may agree that if two plus two equals five, then I am a monkey's uncle".