From the moment Charlie left Hogwarts, he'd heard about Harry Potter. The longer time goes on, the more their lives become intertwined and the more Charlie can't keep himself away (8 year age gap be damned).
This is an AU, but uses as many elements from canon as possible. It follows the order of the books but is mostly from Charlie's perspective. Up until later chapters of the story, this all could feasibly exist within the canon universe.