The question is fairly straightforward: is the passive voice of "I know him," which would be "he is known by me," a valid English sentence? I thought I had heard/read it before, but I may be wrong and it may also be some form of slang.
I am a student of Italian, and in learning the passive voice, I attempted to make this same connection and was told that this is not a valid passive voice in Italian because "to know" ("sapere" in Italian for those interested) cannot be used in the passive voice.
This idea is mentioned in this question, but I struggled to find a definitive answer.