coup de foudre (noun) 

Coup de foudre (koo duh FOO-druh), a French expression, literally means thunderbolt. It is often used to describe a sudden unforeseen event – in particular, love at first sight. As used by Susan Choi in My Education: “Coup de foudre; perhaps it was real. One went from believing, when twenty, that it was the kind of love that was real, to believing, once closer to forty, that it was not only fragile but false – the inferior, infantile, doomed love of twenty-year-olds.”