Will Smith shared a screen grab of himself and Janet smiling and laughing at each other, which might make ya think hell is about to freeze over ... because that's basically what she said would happen before this reunion could happen.

Hubert, who played Aunt Viv for the first 3 seasons, has repeatedly said she hated Will and blamed him for her firing. In fact, back in 2011, she said, "There will never be a reunion ... as I will never do anything with an a**hole like Will Smith."

Thankfully, somehow, they've buried the hatchet. Will also posted a pic of the rest of the fam gathered to shoot the special -- Alfonso Ribeiro who played Carlton, Tatyana Ali who played Ashley, Karyn Parsons who played Hilary, Joseph Marcell who played Geoffrey Butler the butler, DJ Jazzy Jeff who played Jazz and Daphne Reid who played v.2 of Aunt Vivian.

The only missing cast member was Uncle Phil ... you'll recall James Avery, passed away in 2013.

The 'Fresh Prince' reunion is expected to air on HBO Max sometime around Thanksgiving -- and don't forget about the new 30th Anniversary clothing line, which just launched. Talk about master marketing.

Will's got this teaser thing down pat, 'cause everyone's dying to know how he and Janet squashed their beef.