原来 (so it turns out / all along)

So that's why

• Your colleague hasn't touched his lunch all week. Today you find out he has a toothache.
• so it turns out原来yuán láihe他tā牙疼yá téng，no wonder难怪nán guàinot不bùto have a meal吃饭chī fàn。 — "So he has toothache — no wonder he isn't eating."

so it turns out原来yuán lái = so it turns out

• so it turns out原来yuán lái announces a discovery: the truth you have just found out explains something.
• It usually starts the clause: so it turns out原来yuán láiit's是shìyou你nǐ！ — "Oh, it's you!"

so it turns out原来yuán láiit's是shìyou你nǐ！

Discovery and explanation

• I / me我wǒto think (i.e. to take it…以为yǐ wéihe他tāit's是shìteacher老师lǎo shī，so it turns out原来yuán láihe他tāit's是shìstudent学生xué shēng。 — "I thought he was a teacher, but it turns out he's a student."
• Often with no wonder难怪nán guài (no wonder): so it turns out原来yuán láisnow下雪xià xuě(completed / change)了le，no wonder难怪nán guàiso这么zhè mecold冷lěng。

so it turns out原来yuán láisnow下雪xià xuě了le，no wonder难怪nán guàiso这么zhè mecold冷lěng。

Two meanings

so it turns out原来yuán lái = originally

• he他tāso it turns out原来yuán láilive住zhùin在zàiBeijing北京Běi jīng，afterwards后来hòu láito move (i.e. relocate…搬bānto / arrive到dào(completed / change)了leShanghai municipality…上海shàng hǎi。 — "He originally lived in Beijing; later he moved to Shanghai."
• Here so it turns out原来yuán lái contrasts the earlier situation with a later change.

he他tāoriginally原来yuán láilive住zhùin在zàiBeijing北京Běi jīng。

Recap

Read the full reference: HSK 4 grammar — Adverbs.