On Saturday, they'll meet again on Causeway Street. But this time, it'll be as divisional rivals.
Swayman is expected to square off against Ullmark for the first time as the Bruins take on the Ottawa Senators.
"It still hasn't hit," Swayman said. "It still feels like I've got his presence around here and the traditions that we had still live on. And that's with every guy that's been through this locker room. ... We're brothers for life."
With both Ullmark and Swayman on the depth chart for three seasons, the Bruins racked up wins; the two goalies combined for a record of 160-56-25 as teammates.
The presence of Ullmark -- who took home the Vezina Trophy in 2022-23 -- allowed Swayman to ease into NHL reps and develop on his own timeline.
"It goes to show what kind of character he has," Swayman said. "Just his awareness to pick up those guys around him and see what he could help with -- with the experiences that he's gone through, and shed some light so I wouldn't make the same mistakes or would have a little bit of a better way in different situations.
"I'll forever be grateful for that and he knows that, and I still will call him if I have questions. And it's really great to see the success that he's had and will continue to have because of what he has between the ears."
Swayman planned on carving out some time to meet up with Ullmark Friday, but on Saturday it will be business as usual for a Bruins team looking to right the ship amid a 7-7-1 start.
Both Swayman and Ullmark have yet to settle into their roles. Swayman is 4-5-1 as the Bruins' No. 1 netminder with an .894 save percentage, although his numbers have been hurt by a leaky penalty kill. He is among the league's worst in save percentage during shorthanded situations (.793).
Ullmark has labored with Ottawa, especially after missing a few games because of injury. Since returning Oct. 25, he has lost four of his last five games while sporting an .873 save percentage over that stretch.
Asked by reporters in Ottawa Friday where he feels his game is, Ullmark said, "I do not know. I do not know if it's in a good place or a bad place. All I know is that, for me, it's going to be exciting to go in there tomorrow and battle my heart out."
Given that Ullmark and Swayman now don different sweaters, it seems unlikely that they will embrace on the ice again.
"I guess you'll have to wait and see," Swayman said with a laugh. "Keep you on your toes."
The Bruins' decision to deal Ullmark was based on their desire to elevate Swayman into a No. 1 role and free up cap space to hand him a hefty contract.
But they also landed three players in return: Joonas Korpisalo, Mark Kastelic, and a first-round pick (No. 25 overall) that became Boston College center Dean Letourneau. The return has yielded encouraging results so far, headlined by Kastelic.
"I think his offensive potential is much more surprising than I expected," said Bruins coach Jim Montgomery. "His compete, his willingness to be hard in all three zones, is something that we had seen when we played against him when he was in Ottawa."
While Kastelic's physicality (a team-leading 64 hits) and proficiency in faceoffs (55.0 percent) have been as advertised, he's also added some much-needing scoring punch in the bottom six (three goals and four assists over 15 games). He is just 4 points shy of matching his career high.
Despite concerns over Korpisalo's viability as a backup goalie after a disastrous stint in Ottawa last season, he has been steady so far. Over his last four appearances, he has a .933 save percentage -- and a shutout win over the Flyers.
The most valued return in the trade was that first-round pick, with the Bruins hoping that the 6-foot-7-inch Letourneau develops into a legitimate top-six pivot in due time.
Patience will need to be prescribed, as he is considered a project after developing at the prep school level and accelerating a year at BC. Letourneau has one assist over five games with the Eagles.