Former New England Patriots offensive coordinator Bill O’Brien revealed some secrets as to how the Patriots offense was functioning at a high level with Rob Gronkowski and Aaron Hernandez as the tight ends.

He sat down with Jon Meterparel on The Bill O’Brien Podcast with Jon Meterparel and admitted teams didn’t know how to play against the Gronkowski and Hernandez duo.

“When we got Hernandez and we went 12 personnel, then teams didn’t know how to play us,” said O’Brien. “They would try base, and we would run them out of that with passes. And then they would go to nickel, and we could run it or throw it. Then, they would go to dime, and Bill Belichick was a genius on the sideline when it came to this stuff. He’s like ‘They’re going dime, go fast, you’re trapping them in dime.’ So, we would trap teams in dime and just go tempo and run the football.”

Gronkowski and Hernandez came into the league together in 2010. They played three seasons with one another and formed one of the greatest tight end duos of all time. It would be hard to find a greater mismatch for a defense than having to deal with Gronkowski and Hernandez at the same time. They were a true nightmare matchup for opponents.

Hernandez was arrested and indicted on murder charges, abruptly ending his career with 175 receptions for 1,956 receiving yards and 18 touchdowns. Meanwhile, Gronkowski went on to win four Super Bowls in a career where he posted 621 receptions for 9,286 yards and 421 touchdowns. Many believe he is the greatest tight end in NFL history.

One can only imagine how unstoppable the duo might have become if they had played with each other longer.

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This article originally appeared on Patriots Wire: Ex-Patriots OC makes admission on Rob Gronkowski-Aaron Hernandez duo