In an offseason where the New England Patriots lost Tom Brady, Stephen Gostkowski and several core defenders, their trade of Duron Harmon might have been the most surprising development.

The veteran safety had become a key cog in a strong Patriots secondary since the team drafted him out of Rutgers in 2013 and started a career-high eight games in 2019.

So, why did head coach Bill Belichick ship Harmon to the Detroit Lions earlier this month just to move up a couple rounds in the 2020 NFL Draft?

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Joining former Patriots teammates Devin and Jason McCourty on their "Double Coverage" podcast Sunday, Harmon revealed what Belichick said to him about the deal.

"(Belichick) told me, ‘Look, it's just at the point where we have to make some moves and we just paid Dev; it’s just going to be really tough to really do anything, or get anything done in free agency if we don’t do this.' "

That's a candid explanation from Belichick, who had just handed Devin McCourty (Harmon's close friend) a two-year contract worth $23 million.

Harmon, who becomes a free agent in 2021, carries a $4.25 million cap hit in 2020. Given New England's current depth at safety -- McCourty, Patrick Chung and Terrence Brooks are all returning -- and lack of cap space, Belichick apparently believes Harmon's money will be better spent elsewhere.

Harmon will reunite with his former defensive coordinator in Lions head coach Matt Patricia, though, and said he has no hard feelings about the move.

"He was just telling me it’s going to be a great opportunity for me (in Detroit)," Harmon added of Belichick. "I respect that because at the end of the day we know Bill is going to do what is best for the team and I respect that because not a lot of people can do that and have that commitment and dedication that the team is first."