“Ms. Hunter first told the tale of her campaign coup de foudre (“a magnetic force”) and the resulting daughter, now 2, in an interview in the April issue of GQ that was illustrated with sexy pin-up shots of Ms. Hunter lying on a bed in pearls, a white shirt and no pants.”
Prolagus is right (and we also say "a bolt of lightning"), but you do not necessarily need to translate this expression. Although not common, the phrase coup de foudre, which is found in English dictionaries, could be used as it is in a sophisticated English text just as we use other French expressions (e.g. pièce de la résistance, coup de grâce, par excellance) in English.