原来 + Clause
The adverb 原来 (yuánlái) means 'it turns out,' 'originally,' or 'so that's how it is.' It is used to express the discovery of something previously unknown or to refer to a former state of affairs. It often introduces new information that explains a situation.
原来是你啊,我刚才没认出来!
Yuánlái shì nǐ a, wǒ gāngcái méi rèn chūlái!
Oh, it's you! I didn't recognize you just now!
原来他已经搬走了,怪不得找不到人。
Yuánlái tā yǐjīng bān zǒu le, guàibùdé zhǎo bú dào rén.
So he had already moved away — no wonder nobody could find him.
这里原来是一片农田,现在变成了商场。
Zhèlǐ yuánlái shì yí piàn nóngtián, xiànzài biàn chéng le shāngchǎng.
This place used to be farmland, but now it has become a shopping mall.