"Gronk" announced his departure from football Sunday on social media. The five-time Pro Bowl selection, four-time All-Pro and three-time Super Bowl winner played nine seasons with the Patriots after being selected in the second round of the 2010 NFL Draft.
He was teammates with Brady for exactly half of the quarterback's Hall of Fame career.
"What an honor and privilege to play with you these past nine years 'Gronk!' You accomplished so much and our team was almost unbeatable when you were on the field," Brady wrote Sunday on social media.
"Your fun-loving, inspiring, and positive energy made an impact on everybody you came into contact with! Not just that, but for as great as a player you are, you are a better teammate and person. The NFL was a better place with you in it! But I have no doubt you will be a success in anything you do!!! Love you pal!"
"In the nine years that I have known Rob Gronkowski, I have never known him to have a bad day," Kraft said in a statement from the Patriots. "He always has a youthful exuberance about him and is a joy to be around. As a player, he earned the respect of his coaches and teammates for his hard work, preparation, selfless attitude and the sheer dominance of his game. 'Gronk' quickly became a fan favorite and the most dominant player at his position for nearly a decade. I look forward to honoring him in the near future as both a Patriots and Pro Football Hall of Famer."
Kraft also said Gronk was an even better person than he was a player.
"It was a pleasure and a privilege to coach Rob Gronkowski the past nine years," Patriots coach Bill Belichick said. "From his rookie year until his final season and through countless times in between, Rob was a major reason why we won games and championships. His elite combination of size, skill, intelligence, toughness and ability to perform in pressure situations set him apart."
"Rob's impact on our team and organization was felt in many ways. In the ultimate team sport, Rob was a great, great teammate. His production spoke for itself, but his daily attitude, unmistakably positive energy wherever he went and toward whoever he touched will never be forgotten."
While Gronkowski said he was retiring, his agent Drew Rosenhaus speculated that Gronkowski could change his mind.
"Young guys, they can change their mind," Rosenhaus told ESPN Monday. "Never know."