原来
Meaning
原来 has several uses: 1. Noun — “the past”, “formerly”. 2. Adjective — “original”, “former”. 3. Adverb — “formerly” (things have changed). 4. Adverb — “it turns out”, “so…” (realising something new).
1. 原来 as a noun
坐火车从北京到上海，原来最快差不多需要十二个小时，现在有了高铁，五个小时就能到
2. 原来 as an adjective
原来的 + Noun
按原来的计划应该是两周，但是我们可以提前完成
3. 原来 as an adverb (formerly)
她原来是汉语老师，现在已经成了一名律师
4. 原来 as an adverb (realisation)
Shows the speaker discovering something they didn't know. 原来 can go before or after the subject.
马克一直等李明回电话，可是电话一晚上都没来，原来李明把马克的电话号码记错了
原来 vs. 本来
原来你会说中文！
我本来想去
原来 → a former situation, or a newly discovered fact.
本来 → the original plan, or what ought to have been.