What difference in meaning or otherwise does the inclusion or omission of the definite article make in this sentence?
When that day comes, you will be (the) first to know.
I would like to add that in Ngram, the results are pretty comparable.
Learn English – “The first to know” Vs. “First to know”
definite-article
Best Answer
If you said to me, "When that day comes, you will be first to know." I would understand it to mean when the day comes I will be the first one you tell. i.e you will know the day has come and the first person you tell will be me. Whereas, if you said, "When the day comes, you will be the first to know." I would take to mean I will know the day has come before anybody else, including you.