に至って (ni-itatte): Only upon reaching; when it comes to
～に至って (ni-itatte)
Meaning
Only upon reaching; when it comes to
Formation and usage
N／V dictionary + に至って（は／も）
Notation: N = noun; V dictionary = dictionary-form verb; V stem = the stem before ます; plain clause = plain-form clause; negative stem = the form before ない. Follow the attachment shown above.
Explanation
Marks a final or extreme stage; with 初めて it means only then, and with は it singles out a case.
Examples
会議が中止になるに至って、初めて問題の深刻さに気づいた。
Only when the meeting came to be canceled did I realize how serious the problem was.
試験が中止になるに至って、初めて問題の深刻さに気づいた。
Only when the exam came to be canceled did I realize how serious the problem was.
研修が中止になるに至って、初めて問題の深刻さに気づいた。
Only when the training session came to be canceled did I realize how serious the problem was.
発表会が中止になるに至って、初めて問題の深刻さに気づいた。
Only when the presentation event came to be canceled did I realize how serious the problem was.
面接が中止になるに至って、初めて問題の深刻さに気づいた。
Only when the interview came to be canceled did I realize how serious the problem was.
How related patterns differ
に至って emphasizes a final or extreme point; にして初めて achieves a result only at that stage. ぬ間に uses the time before a change. に至るまで extends a range, while をめぐって surrounds an issue with activity or debate.