TAKOBOTO

Just as one is about to start doing something
Just as I was about to leave the house, it started raining

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わたしがへんじをしようとしたやさきに、かれがくちをだしてきた。

I was about to reply, when he boldly cut in.

ちちがでかけようとしたやさきにでんわがなった。

My father was about to leave when the telephone rang.

The title of the linked page offers corroboration that the phrase is JLPT 1: https://j-nihongo.com/yasakini/

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