东dōng窗chuāng事shì发fā

Literal: the east-window affair comes to light
Figurative: For a secret scheme or misdeed to come to light, leaving its author to face the music; used in earnest and also in jest.

Where does 东窗事发 come from?

It comes from a legend about Qin Hui, the Southern Song chief minister blamed for the death of General Yue Fei, recorded in 《钱塘遗事》 by Liu Yiqing 刘一清 (Yuan dynasty). According to the tale, Qin Hui plotted Yue Fei's death with his wife beside the east window of their house. After Qin died, a Taoist priest performing rites at his widow's request saw him in the underworld wearing an iron cangue, and Qin asked him to tell his wife that the east-window affair had come to light. It is legend, not history. Today it is said when something shady is uncovered.

Source (出处): 刘一清《钱塘遗事》

How is 东窗事发 used? Two examples

他tā挪nuó用yòng公gōng款kuǎn好hǎo几jǐ年nián，这zhè次cì审shěn计jì终zhōng于yú东dōng窗chuāng事shì发fā了le。
He'd been embezzling public funds for years, and this audit finally blew the lid off it.
我wǒ偷tōu吃chī了le妹mèi妹mei的de蛋dàn糕gāo，没méi想xiǎng到dào当dàng天tiān就jiù东dōng窗chuāng事shì发fā。
I secretly ate my little sister's cake, and wouldn't you know it, I got found out that same day.

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