The sentence is as follows:
You see, when Elvis died, he _ (already, be) super famous for years.
You have to use the verb in the bracket and put it into the right tense. I've used the past simple, which would be:
You see, when Elvis died, he already was super famous for years.
But the key states otherwise:
You see, when Elvis died, he had already been super famous for years.
Was i completely wrong or is my answer also viable?