EXCLUSIVE

Sorry to crush the dreams of everyone hoping to see 49-year-old Brett Favre unretire (again) and suit up for 2020 ... the Gunslinger tells TMZ Sports his Instagram was HACKED.

Football fans lost their minds after Favre's verified IG account posted a throwback pick from Super Bowl XXXI with the caption "A true champion sticks to his or her calling. I will be coming out of retirement and making my return to play in the NFL for the 2020 season."

The post was deleted minutes later ... leaving people to speculate whether Favre was really coming back again.

Look, we've seen Favre throw passes recently and the guy still has a cannon for an arm. In fact, in late 2017 Favre told TMZ Sports he was confident he could still make NFL throws but didn't want to take the hits anymore!!!

Had the G.O.A.T. Brett Favre out throwing today. I asked him to come out retirement to throw a pick to me. J/P cool guy... #TAT pic.twitter.com/FljsvBSIXh @rockorocky

So, when we saw the new Instagram comeback post, we had to call him up to see if he was REALLY trying to get back in the league ... but alas, it was not meant to be.

Favre says the explanation is simple -- someone hacked his social media account -- he's not trying to pull a Rafael Palmeiro and play pro ball into his 50s.

Now, Favre says the phony post was deleted and his team is scrambling to find the culprit.