Wiktionary
long since
adv. (context idiomatic English) long ago; in the (distant) past.
WordNet
Usage examples of "long since".
The awful, interminable flapping of their wings, the ceaseless tempo of their movement, had long since dulled her mind to any chance of potential rescue.
He knew that everyonemost especially the lady he had loved more than his own lifefor whom he had held any degree of affection had long since ceased to exist.