It feels like forever ago, but it really wasn't that long ago when Eric Mangini and Bill Belichick paired up as one of the league's best coaching duos. From 2000-04, Mangini served as the Patriots' defensive backs coach before taking over as the defensive coordinator in 2005. In those six seasons, the Patriots won 63 regular-season games and three Super Bowls.

And then it all went to hell. Mangini left for the Jets and started what became known as Spygate, a scandal that cost the Patriots a first-round draft pick and money, and ultimately branded them as cheaters.

Speaking with the New York Post's Brian Costello in an article that was published Tuesday, Mangini -- now out of the NFL -- opened up on his damaged relationship with Belichick. He admitted that he regrets Spygate.

From the Post's article:

"Spygate is a big regret," Mangini said. "It wasn't supposed to go down the way it went down."

Mangini warned Jets security that the Patriots could be videotaping the Jets' signals during their game at Giants Stadium on Sept. 9, 2007. He knew this from his time in New England. Mangini wanted the Patriots stopped, but he never thought it would get reported to the league.

But Tannenbaum reported it to the NFL, and Spygate was born. The NFL fined Belichick $500,000 and the Patriots $250,000. They also were stripped of their first-round pick in the 2008 draft.

"There was no great value in what they were doing," Mangini said. "It wasn't worth it. It wasn't worth it to me personally. It wasn't worth it to the relationship."

Mangini went on to explain why he did report it, even if he acknowledged that the Patriots weren't gaining much by taping teams: because he didn't want to put the Jets at a competitive disadvantage, which makes sense. He added, however, that he cared about Belichick and the Patriots and didn't want to hurt them.

So clearly, he still regrets how his relationship with Belichick ended. He revealed to the Post that he hasn't held a real conversation with Belichick in a decade. In that same story, Mangini also offers some interesting insight into the brief Brett Favre era -- so go read it -- but let's stick with Spygate.

Though Mangini shouldn't feel bad for ratting out Belichick -- he would've been doing his team a disservice had he allowed the Patriots to film his signals -- he unintentionally ruined the Patriots organization's reputation. Would Deflategate really have mattered or generated any kind of interest if it had involved, say, the Bills or the Chargers? Because Spygate was already on the Patriots' record (and because they win, a lot), Deflategate turned into a giant scandal, even though the PSI levels of a few footballs hardly mattered in a blowout of a game.

Again, I'm not saying the Patriots were blameless in Spygate. I'm also not saying the Jets were wrong to report the Patriots. I'm guessing the other 30 teams were thankful they did that.

But from Mangini's perspective, the regret makes sense. He lost one of his friends and mentors, and he's no longer coaching in the NFL after his recent stint as the 49ers' defensive coordinator ended last year.

Meanwhile, Belichick is doing just fine in his post-Mangini years. He won another Super Bowl and remains the best coach in the league -- exemplified by the Patriots' 3-0 start without Tom Brady.