Come il simple, ma mette l'accento sulla durata di ciò che era in corso prima di quel momento passato.
Come si forma
had been + verbo in -ing.
- I had been waiting for an hour when the train finally arrived.
- She was tired because she had been working all night.
Attenzione
Vale la stessa regola di sempre: i verbi di stato non vanno al continuous.
- I had known him for years. ✅
- I had been knowing him for years. ❌