The New York Rangers and their young Norris Trophy-winning defenseman, Adam Fox, have agreed to a historic contract extension.

Fox, 23, signed a seven-year deal on Monday, taking him through the 2028-29 season. Terms weren't disclosed by the team, but a source tells ESPN the average annual value of the contract is $9.5 million against the NHL salary cap. He's in the last year of his entry-level contract this season.

The $66.5 million deal is the largest contract in NHL history for a defenseman leaving his entry-level deal.

Fox has 98 points in his first 134 games, putting together two outstanding seasons with the Rangers. Fox was fourth in the rookie of the year voting for 2019-20. Last season, he won the Norris Trophy as the NHL's top defenseman with 47 points in 55 games.

So far in 2021-22, Fox has nine points in nine games, tied for second in the NHL among defensemen. He's skating 24:16 per game on average. On Sunday night, he scored the winning goal in the third period of a 3-1 victory over the Seattle Kraken.

"We are thrilled that we have agreed to terms with Adam on a contract extension and that he will continue to play for the team he grew up cheering for," Rangers general manager Chris Drury said. "In just over two seasons, Adam has consistently shown why he is a cornerstone for our organization and one of the best players in the NHL. It has been a privilege for us, and our fans, to watch Adam showcase his ability on a nightly basis, and we are glad to have that opportunity for seven more years."

The former Harvard defenseman is the latest young blueliner to break the bank on his second contract. Fox joins Zach Werenski of the Columbus Blue Jackets ($9,583,333 AAV), Charlie McAvoy of the Boston Bruins ($9.5 million AAV), Cale Makar of the Colorado Avalanche ($9 million AAV), Miro Heiskanen of the Dallas Stars ($8.45 million AAV) and Quinn Hughes of the Vancouver Canucks ($7.85 million AAV) as defensemen under the age of 25 who have signed new contracts in the last year.