Manning thought it was important enough to say goodbye to Belichick in person, knowing full well that there were plenty of cameras around that could eventually reveal his intentions.
And on Sunday night, Belichick returned the favor.
"It is with great admiration that I congratulate Peyton Manning for his tremendous career in the National Football League," the Patriots coach told ESPN.com. "Peyton raised the bar as a performer and as a competitor and with a personal class in which he carried himself off the field. My relationship with Peyton is special, it is unique and it is one that I value greatly.
"For 18 years, we battled fiercely but regardless of each game's outcome, I always walked off the field with the utmost appreciation for the highest level of competition in which those games were prepared for and played. Peyton's immense contributions to the game reflect how genuinely passionate he is about it. I can honestly say that I never 'enjoyed' our meetings, but the respect I have for Peyton Manning as a competitor was, and will likely remain, second to none."
Manning ended up 6-13 all-time against the Patriots and played New England more than any team outside of the Texans, Jaguars and Titans. Even though Belichick's record is far superior, there is an inherent level of respect there. Manning was one of the few players who pushed the game forward on a similar level to Belichick over the past two decades.
The rivalry between Manning and Tom Brady always received top billing, but it was Belichick -- a coach with defensive roots -- who actually stayed up all night trying to stop Manning's revolutionary frantic offense. Those moments ended up providing viewers with some of the best games with high stakes over the past 20 years.
In the lead-up to their final matchup, Belichick was asked about Manning's apparent decrease in arm strength and struggles throughout the 2015 season. He said that under no circumstances would he ever bet against Manning. His statement Sunday night was a mix of pure admiration and relief. The quarterback who caused Belichick more aggravation than any other is gone now.