So I was helping my friend with her English and she asked me to explain this question:
When did you first meet him? -> How long have you met him?
I know the form When did + Subject + first + Verb => How long have/has + Subject + Past Participle is correct but I just think the sentence How long have you met him sounds a little bit wrong and I just want to explain it correctly to her so if anyone can help me check if the sentence is correct and explain it to me I'd be very thankful.