TB12 shared his thoughts about the huge Patriots news in a lengthy Instagram post on Thursday ... saying Belichick was "a great leader for the organization, and for all of the players who played for him."

"We accomplished some amazing things over a long period of time, many of which will be hard to replicate."

Brady and Belichick were one of the greatest combos in NFL history -- they led the Pats to 19-straight winning seasons and 17 division titles during their time together.

They also appeared in nine Super Bowls ... taking home the Lombardi Trophy six times.

"He worked every day to help us achieve the ultimate goal, in the ultimate team sport," Brady continued. "And, although we were successful, some of the greatest lessons, I learned, were in the moments where we faced the most challenging adversities."

"I could never have been the player I was without you Coach Belichick. I am forever grateful. And I wish you the best of luck in whatever you choose next."

It seems to put an end to any speculation there could still be bad blood between the two ... as many believed Bill played a large role in Brady's departure to the Tampa Bay Buccaneers in 2020.

Brady also had BB's back during the season ... saying the Pats' struggles were not his fault.

Belichick also poured his heart out at Thursday's press conference ... saying he's grateful for the 24 years in NE, the coaching staff, players and especially the fans.

"Fans here are amazing," the 71-year-old said. "So many memories of fans, the send-offs, the parades, the Sundays."