Barstool's Dave Portnoy on Tom Brady Leaving Pats, 'The World May Be Ending'

Barstool Sports president Dave Portnoy is coming to terms with the fact Tom Brady is no longer a New England Patriot ... and he's convinced this could be the end of the world as we know it.

Remember, El Pres told TMZ Sports less than a month ago ... "Anybody who says (Brady's) going anywhere is an idiot!!" ... and obviously, TB12's leaving.

We reconnected with Portnoy in wake of the news on Tuesday ... and despite the devastating news, the guy is actually taking it well.

"I wasn’t stunned," Dave tells us. "I thought he would come back to New England, because I think we offer him the best chance to win ... it’s sad, it’s the end of an era."

"This is the real world. We got corona running wild in the streets, things happen. So, Brady’s leaving the Patriots. Crazy times. .. the world may be ending."

Pres makes it clear he still LOVES Brady and isn't pissed he's leaving the Pats ... but believes TB12 just ain't a franchise QB anymore.

"If you’re a Patriots fan and you care about winning in the next 10 years, this is the right move … if you only care about the next 2, then you probably want Brady."

Portnoy says he believes in Bill Belichick and likes the Pats' chances of winning a title before TB12 (regardless of which team he chooses) ... but his love for Brady will live on.

As for Brady's replacement?? Portnoy's got a guy in mind -- and the dude once defeated TB12 at the highest level.