I have a friend who recently wrote to me and used the following sentence:
Je n'en pouvais plus de cet exil.
I understand the meaning, but I remain confused about the use of en. As I've used it before, I would have used en to replace something that is introduced by de (e.g. J'ai mangé des pommes. --> J'en ai mangé.) or a countable noun that was previously introduced and clear to the reader/listener (e.g. J'en ai un.) In this case, it isn't clear to me if en is referring to cet exil, in which case, why is cet exil still necessary in this sentence? He hadn't mentioned this before, so Je n'en pouvais plus would have been confusing to me. Mainly, I am looking for help to deconstruct this sentence and to understand the use of en in this case, and when it is used in addition to the noun/concept it is referring to.