He texted New Jersey Devils defenseman Will Butcher, who was in town for a game against the Stars the next night, to see if he wanted to get together for dinner.
An NHL coach socializing with a player from the other team the night before their teams play against each other is certainly not normal behavior, but to Montgomery, their dinner was a chance to catch up with a friend he's known since he sat in his living room on a recruiting trip years ago.
Butcher played four seasons for Montgomery at the University of Denver from 2013-17. The Pioneers won the NCAA championship in Butcher's senior season, when he also won the Hobey Baker Award as the best player in college hockey.
"It's a pretty special relationship you've cultivated," Montgomery said.
The relationship didn't get tossed aside because they're opponents and Montgomery had to come up with a game plan against Butcher and his team (Dallas defeated the Devils 5-4, and Butcher had two assists).
One of the many things Montgomery and New York Rangers coach David Quinn, who spent the past five seasons as coach at Boston University, have discovered this season is that coaching in the NHL is not at all like coaching in college, mostly because of the different relationship with the players.
In college, Quinn and Montgomery's recruiting trips would take them into homes of teenage players with the hopes of forging deep, lasting relationships with them and their families. Once Quinn or Montgomery got a player to commit, he had him for four years unless he transferred or left early to turn pro.
In the NHL, their players are already adults and professionals, some with families of their own, who work with them because it's their job. They can be here one day and gone the next because of trades, waivers, demotions and free agency.
"It's different, man," said Quinn, who was an assistant at BU from 2004-09. "You never lose that connection [to your college players]. What makes college coaching unique is those are lifelong relationships."
Quinn has already coached against former BU players including: Buffalo Sabres center Jack Eichel and forward Evan Rodrigues; Arizona Coyotes forward Clayton Keller; Ottawa Senators forward Brady Tkachuk; Nashville Predators center Nick Bonino; and Colorado Avalanche forward Colin Wilson.
Quinn will make his first return to Boston as an NHL coach when the Rangers play the Boston Bruins at TD Garden on Saturday (7 p.m. ET; NHLN, NESN, MSG, NHL.TV). He'll go up against three of his former BU players: defensemen Charlie McAvoy and Matt Grzelcyk, the captain from 2014-16, and forward Jakob Forsbacka Karlsson.
He has already circled the game against the Minnesota Wild at Madison Square Garden on Feb. 21, because that's the first time he'll see Wild forward Jordan Greenway, who played under him at BU the past three seasons.
"I mean, Nick Bonino, I went to his wedding, he's a close friend of mine," Quinn said. "Colin Wilson too. I recruited them. These guys are friends. To see [Keller] and Jack and Rodrigues, it's different. Greenway is going to be tough. Charlie is going to be tough. I'm really close with them."
Montgomery, who has coached two NHL games against Boston forward Danton Heinen, his player at Denver from 2014-16, said the dinner conversation with Butcher focused more on their personal lives than about hockey.
"I would say it's 90 percent you're talking as friends now," Montgomery said.
Montgomery said Butcher asked for his address, which means he'll likely be getting an invitation to defenseman's wedding.
"It's just the relationship that we forged over my four years there," Butcher said. "It just makes it seem like you're seeing an old buddy. That's kind of what it was."
Quinn hasn't had dinner with a former player yet, but he said he'd do it and he wouldn't care if people thought it to be strange or uncommon.
"I wouldn't even think twice about it," Quinn said.
That wasn't always true. Quinn said he turned down dinner invitations from former BU defenseman Kevin Shattenkirk, now of the Rangers, and Wilson during his one season as an assistant with the Avalanche (2012-13).
"I'm like, 'I can't, just can't,'" Quinn said. "We're walking in and I say to (former Avalanche coach) Joe Sacco and (assistant) Timmy Army, 'I miss being able to do that.' "
Quinn left to coach BU after that season.
The situation arose again last May when Quinn took over as Rangers coach. He had already accepted an invitation to attend Shattenkirk's wedding in July but questioned whether he should still go.
"And then it was like, 'Why wouldn't I?'" Quinn said. "That's part of the problem, I think, in pro sports. Like, why wouldn't I go? There's a human element to all of this and I think people lose sight of that."
Quinn and Montgomery haven't, even though they're competing against their former players. If anything, their relationships with their former college players are stronger now because they're not on the recruiting trail anymore.
"Greenway was texting me an awful lot earlier in the season and I said, 'Hey, you do know I coach the Rangers now,'" Quinn said, laughing. "Listen, I'm not going to apologize for it. Not a chance. Those guys mean an awful lot to me and they always will.
"The Boninos, I saw them after we played Nashville, and they came running over with big hugs. That's the level of the relationships."