Nobody was tweeting in those days..
We don't know how long he lived or if he perished in the war of 66-70 AD - listen to what Paul told them in regards to the "man of sin":
2 Thess 2:5 Do you not remember that while I was still with you, I was telling you these things?
Paul had already addressed the "man of sin" issue and it's quite possible he spelled out who he was.
But the point of him telling them is it was more than probable that his "unveiling" would have a direct effect on them.
He's not prophesying of something way off in the future.