"It wasn't about numbers or money," Horton's agent Paul Krepelka told ESPN The Magazine, adding that it was a chance for a fresh start.
Horton is coming off a pedestrian regular season in which he registered 22 points in 43 games but found his game in the postseason, where he had seven goals and 12 assists in 22 games during the Bruins' run to the Stanley Cup finals. He was also a plus-20, which led the NHL playoffs. In 43 career playoff games, Horton has 15 goals and 21 assists, including six game-winning goals.
"Nathan has done very well for us, especially in the playoffs," Bruins president Cam Neely said Friday. "He's scored some big-time goals and has made a huge impact. We like the way that line plays and we certainly would like to have Nathan back, but this is a challenging year coming up with the cap dropping as much as it does."
The 6-foot-2 winger's last contract was a six-year deal that averaged $4 million per season and he should earn at least that much on the open market. Free agency opens on July 5.
During the team's exit meetings Wednesday, Horton had told Chiarelli that he would be open to returning to Boston.
"With him being unrestricted, certainly you want to have those conversations fairly quick and see where they're at and where we're at and need to be at, especially for next season," Neely said. "That's certainly pressing, but everything's pressing right now."
With the heads-up of his departure, the Bruins' next move is expected to be to trade his negotiating rights rather than let him leave without getting anything in return.
ESPNBoston.com Bruins reporter Joe McDonald contributed to this report.