Even with long-existing rumors that Rob Gronkowski was considering retirement, Sunday's news that the Patriots tight end was calling it quits came as somewhat of a stunning development for many.

Gronkowski announced the news via a lengthy Instagram post and thanked the Patriots, his fans and teammates for their support on his journey. The tight end spent all nine years of his excellent NFL career in New England, and he has the distinction of going out as a champion -- actually, a three-time champion -- following the Patriots' Super Bowl LIII victory in February. His final catch was a pivotal red zone grab that helped set up the Pats' only touchdown against the Rams.

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It all started at 20 years old on stage at the NFL draft when my dream came true, and now here I am about to turn 30 in a few months with a decision I feel is the biggest of my life so far. I will be retiring from the game of football today. I am so grateful for the opportunity that Mr. Kraft and Coach Belichick gave to me when drafting my silliness in 2010. My life experiences over the last 9 years have been amazing both on and off the field. The people I have meet, the relationships I have built, the championships I have been apart of, I just want to thank the whole New England Patriots organization for every opportunity I have been giving and learning the great values of life that I can apply to mine. Thank you to all of Pats Nation around the world for the incredible support since I have been apart of this 1st class organization. Thank you for everyone accepting who I am and the dedication I have put into my work to be the best player I could be. But now its time to move forward and move forward with a big smile knowing that the New England Patriots Organization, Pats Nation, and all my fans will be truly a big part of my heart for rest of my life. It was truly an incredible honor to play for such a great established organization and able to come in to continue and contribute to keep building success. To all my current and past teammates, thank you for making each team every year special to be apart of. I will truly miss you guys. Cheers to all who have been part of this journey, cheers to the past for the incredible memories, and a HUGE cheers to the uncertain of whats next.

A post shared by Rob Gronkowski (@gronk) on

Despite a relatively short career that featured a number of significant injuries, Gronk will go down as one of the best -- if not the best -- tight ends of all time. It seems inevitable that he will eventually land in the Pro Football Hall of Fame. Gronkowski garnered plenty of respect during his career, and many current and former players were quick to react to the news of his retirement on Sunday.

Gronk didn't give any hint as to what's next for him in his life after football, only saying that he's excited about the uncertainty of his post-playing career. However, some feel like he'll be heading to the WWE, while others hope he'll be taking Jason Witten's place in the Monday Night Football booth.

Or maybe he's got something else in his future?

We may never see a player like Gronk in the NFL again, but it seems rather likely we'll see plenty of him elsewhere in the coming years.