In standard English I would say that this could be interpreted as "You are that famous person.". I would be surprised if this sentence did not have a higher frequency than "You are that famous one".
Which in Italian would become something like "Sei quel tizio famoso", with "tizio" meaning "guy".
Agree with those who reported it for the reason below. Also, how in Italian would one say "you are that famous?" Idiomatically perhaps?
I'm not sure... You mean "that famous" as in "wow, you are on tv, are you that famous?!"? In that case, it would be "sei così famoso?!"