accidentally; by chance/coincidence/accident; as luck would have it; as it happens; coincidentally
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真碰巧!
What a (happy) coincidence!
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我正要找你,碰巧你来了。
I just want to see you, and by coincidence you came.
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他俩碰巧同时到达。
By chance they both arrived at the same time. / They happened to arrive at the same time.
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事发时他碰巧在现场。
It just so happened that he was there when the accident took place. / He happened to be there when the accident took place.