The moment I met her, I fell in love.
This sentence conveys the meaning that the speaker met a woman and immediately fell in love and looks to be grammatically correct to my eyes.
Now if we changed that sentence to The moment I met her, I soon fell in love., the meaning changes. It now means the speaker met this woman, and not immediately, but soon after, fell in love with her. The sentence sounds weirder than the first one, less idiomatic, but is this second sentence necessarily grammatically incorrect?
We say "the moment x happened/happens, y happened/happens." , but if we said the moment x happened, y soon happened, does the insertion of soon render the sentence grammatically incorrect?