The Matt Snell mystery is solved, why one of the greatest Jets of all time, one of the heroes of their only Super Bowl championship, wants nothing to do with the franchise.

It revolved around the team’s former owners refusing to write him a letter of recommendation for a construction job after his playing days were over. At least, that’s the 77-year-old Snell’s version of his grudge according to excerpts from the Bob Lederer book, “Beyond Broadway Joe: The Super Bowl Team That Changed Football” that were published by Deadspin.

In the book, Snell — the team’s fourth all-time leading rusher (4,285 yards) who scored the only touchdown and ran for 121 yards in Super Bowl III — says part-owner Sonny Werblin promised him if the Jets won a championship, he would have a place with the team for life. But others in the organization didn’t follow through on the promise when Werblin was bought out of his stake in the team.

“I don’t know if Sonny ever communicated what he had promised me to the other owners. I know there were people around the organization that were not happy that Sonny and I were friends, and some of them jumped on the opportunity to say bad things about me when Sonny was gone,” Snell said. “It may be that no one in Jets management knew about Sonny’s promises to me, but in 1974, there was a recession and I was in line for a construction job. I asked the Jets for a reference. They told me they didn’t do that for players. They said they couldn’t do it! Can you believe that? I can’t prove it, but I don’t think any of that would have ever happened if Sonny were in charge. That’s why I don’t get along with the organization now.”

As chronicled by The Post’s Brian Costello three years ago, Snell hasn’t let his hard feelings cease, although everyone who was in power of the team at the time are dead. The team has tried to mend the relationship, inviting him to reunions for the 1968 team and other alumni functions, but he has not returned any phone calls. Now we know why.