I thought from the context that it was clear I meant the second version.
I just met this guy. Idk just doesn't conjure up the idea of someone you once knew. It's just loose language, that's why I was confused.
Also you said you recently met him, then you say you just met him. Which is it?
"The guy I just met who was once my ex-employee." This sentence just feels confusing. I can't tell you why but it does.
A simple "He" would be much clearer.
http://www.verb2verbe.com/conjugation/english-verb/meet.aspx
I thought from the context that it was clear I meant the second version.