In addition to what Clive and MM have said, I would add that the first sentence suggests that you realized who he was only after a period of not realizing that. Neither Clive's reworded second sentence nor your third sentence really carry the same connotation.
Yes, dictionaries can indeed be dangerous sometimes. And not just English ones.
You know, making it a point to use new vocabulary is the best way to get it firmly into your active vocabulary. I remember one time trying to use a new German word I'd recently looked up. My German friends looked at me as if I had three heads and asked me where on earth I'd heard that word. (As I r