The unofficial beginning of The Greatest Dynasty in NFL History came the night Mo Lewis took out Drew Bledsoe, and thereby introduced the world to Tom Brady.

The official start of The Greatest Dynasty in NFL History harkens back to the snow globe that was the Tuck Rule game when the football gods smiled on Tom Brady against Jon Gruden’s Raiders, then Bill Belichick started the kid over Bledsoe in Super Bowl XXXVI, and damn if the kid didn’t shock the world and the Greatest Show on Turf with uncommon poise on the winning field-goal drive at the end.

And the football gods kept smiling on this Tom Brady, kept him all these years alongside Bill Belichick, found him Gisele — except for the two Super Bowls against Eli Manning and the one against Nick Foles and, of course, Deflategate.

There were several other potholes on the road to immortality — the torn ACL knee that cost him virtually the entire 2008 season, the home 2010 divisional-round playoff loss to Mark Sanchez, and certainly Saturday night against Ryan Tannehill and Derrick Henry and the Titans.

And now with Tom Brady, of all people, a free agent, comes a moment of truth that threatens the end of The Greatest Dynasty in NFL History and beckons those same football gods to write a final chapter that could very well ruin an American fairy tale.

The odds that Brady gets to ride off into the sunset like a John Elway, who won his second Super Bowl at age 38 and retired rather than chase a historic three-peat, or Peyton Manning, who retired at age 39 after winning his second Super Bowl, are prohibitive, given his age — 43 next summer — and the state of the Patriots with 20 impending free agents and offensive coordinator Josh McDaniels seemingly ready to fly the coop for his own gig.

Such a sobering reality for Patriots fans offers the most unbridled hope fans of the Jets, Bills and Dolphins have had for the better part of two decades.

As long as Belichick is patrolling the New England sideline, it ain’t over til the fat lady sings.

But there is a real chance now that the song being sung across the AFC East will be “Ding Dong the Witch is Dead.”

Whether Tom Brady, who is no longer Tom Brady as we have come to know him, is Belichick’s quarterback or not.

The report from Fox’s Jay Glazer that Brady isn’t interested in giving the Patriots a hometown discount should surprise no one, given that he has given Bob Kraft hometown discounts throughout his career for the betterment of the team.

But at a time when Brady can hear the stampeding footsteps of his football mortality, it pained him that such loyalty was not a two-way street once Rob Gronkowski retired and then the Josh Gordon and Antonio Brown experiments blew up in the organization’s face.

It was beyond depressing for old Baltimore Colts fans watching the shell of John Unitas finish his Hall of Fame career as a Charger, and it would be very much the same for Patriots fans having to watch their beloved No. 12 play for, say, the Chargers.

There will be a starting quarterback market for Brady’s services that there does not appear to be at this point for Eli Manning. Manning has made it clear that backup quarterback is unappealing to him.

Let’s say that Brady remains determined to play until he is 45.

What might he be thinking?

This much we have learned about Brady: five championships were not enough for him, and neither are six. He will want a team that gives him his best chance to win a seventh Lombardi Trophy.

As constructed, the Patriots are not that team. Julian Edelman will be 34 in May. Special teams ace Matthew Slater will be 35 in September and is a free agent. Devin McCourty will be 33 in August. Left guard Joe Thuney is a free agent. Director of player personnel Nick Caserio could leave for another front-office job.

But the grass wouldn’t necessarily be greener should Brady be summoned to replace Philip Rivers and engage the Rams in a Battle For Los Angeles. It certainly wouldn’t be greener in Miami under former New England defensive coordinator Brian Flores as a mentor to Tua Tagovailoa or Justin Herbert.

If anyone is capable of reconstructing on the fly it is Belichick.

This much we have learned about Belichick: He won’t let sentimentality stand in the way of GOATness.

Would Kraft?

It would kill Kraft to say goodbye to the forever face of his franchise.

But if Belichick makes it clear that he prefers a Life After Tom Brady, or that only a hometown discount from Brady would be feasible, then Brady will have no choice but to leave.

“Certainly, Tom’s an iconic figure in this organization, and nobody respects Tom more than I do,” Belichick said Sunday.

And yet Tom Brady is a free agent anyway.

So there is that.

There is also this: Tom Brady belongs exactly where he is. Patriots fans revere him the way Red Sox fans revered Ted Williams, the way Celtics fans revered Bill Russell, the way Bruins fans revered Bobby Orr.

If there is a will, there should be a way. Tom Brady should retire as a Patriot.