竟然
Meaning
竟然 is an adverb meaning “unexpectedly”, “to one's surprise”, “actually (surprisingly)”. It shows that the speaker did not expect this at all and is surprised by it. It normally goes before a verb or an adjective.
Basic structure
Subject + 竟然 + Verb / Adjective
Examples
这个歌特别好听，最近很流行，你竟然没听过？
来这家饭馆吃饭的人竟然这么多，排队都排到门口外边去了！
回家以后，我才发现，竟然忘了去商场的超市买果汁！
When is 竟然 used?
竟然 is used for: — an unexpected result; — surprise; — disbelief; — something contrary to expectations.
竟然 vs. 居然
他竟然会说十种语言
他居然没告诉我
竟然 → stronger surprise at an unexpected result.
居然 → almost the same, but more colloquial and sometimes carries a note of reproach.
竟然 vs. 原来
我竟然忘了
原来你在这儿！
竟然 → an unexpected result.
原来 → realising how things really are.
Remember:
竟然 = unexpectedly, to one's surprise.
It comes before a verb or adjective.
It expresses the speaker's surprise.