As expected; just as one thought — used when something happens exactly as predicted, often referring to an undesirable outcome.
彼は練習をさぼっていたから、案の定試合でミスをした。
He skipped practice, so as expected he made mistakes in the match.
天気予報で雨と言っていたので、案の定ピクニックは中止になった。
The forecast predicted rain, so as expected the picnic was canceled.
彼女は準備不足だった。案の定、発表はうまくいかなかった。
She wasn't prepared. Sure enough, the presentation didn't go well.