Unexpectedly; surprisingly — used to say something turned out different than expected.
試験は案外簡単だった。
The exam was surprisingly easy.
彼女は案外料理が上手だ。
She's surprisingly good at cooking.
案外早く雨が止んだ。
The rain stopped sooner than expected.
Unexpected; unanticipated — used adjectivally (案外だ) to describe something surprising.
案外だが、彼は数学が苦手ではないらしい。
Surprisingly, he doesn't seem to be bad at math.
案外なことに、会議は予定より短く終わった。
Unexpectedly, the meeting ended earlier than planned.
案外な結果にみんな驚いた。
Everyone was surprised by the unexpected result.