The Celtics celebrated Garnett's career after Sunday's 95-92 loss to the Dallas Mavericks, with the 2004 NBA MVP's jersey officially retired by the franchise.
Allen was among those in attendance, which was significant given the rift that emerged between the pair when he opted to move to the Miami Heat as a free agent in 2012.
"It's good to see Ray Allen here," Garnett said during the ceremony. "Real s***. It's good to see you, man. You next, dog."
The Celtics had won the 2008 NBA title with the pair alongside Paul Pierce, while they were Eastern Conference champions in 2010 during a dominant five-year period before Allen's exit prompted the side to drop off.
"Just because I moved away doesn't mean that relationship, that friendship, ends," Allen said.
"It did center around Kevin and myself because I did get the sense that the people here felt how Kevin felt. Once he accepted me, then the people accepted me. That was the sense.
"I was glad we could do that and people could see, 'We won with this guy in 2008, and that's what matters most'."
Former Celtics head coach Doc Rivers, now with the Philadelphia 76ers, weighed in on the reunion.
"Yeah, that's a big one because that's been a problem, obviously, and the fact that it looks like the fence is finally coming down is really cool," Rivers said. "I'm very, very happy for Kevin, and really cool that Ray came today."
Garnett, who won the 2004 NBA MVP with the Minnesota Timberwolves, finished his 22-year NBA career averaging 17.8 points, 10.0 rebounds and 3.7 assists per game.
The power forward/center was a 15-time NBA All-Star, one-time NBA champion and one-time NBA Defensive Player of the Year (both 2008).
The move, with just over four minutes left in the third quarter at Gainbridge Fieldhouse, saw Morant cut in from the right before leaping over Jalen Smith and slamming in a spectacular dunk that had his team-mates and even opposition fans left in visible awe.
The Grizzlies went on to win 130-112 to make it nine victories in a row, and Morant – who ended with 23 points, 10 assists and three rebounds – agreed the dunk was the best of his career so far.
"Yeah, easy," he said. "It's what everybody has been waiting for. I finally made it."
Kevin Durant and Kevin Garnett were among those to react on Twitter to Morant's effort, with the latter exclaiming: "When we look back on Ja's in game dunk highlights when it's all said and done it's gonna be up there with some of the greatest ever."
Desmond Bane, who top-scored for the visitors with 25 points, also acknowledged the effort of his team-mate, saying: "I ain't seen nothing like that one. That's probably going to go down as dunk of the year."
Memphis' win streak has taken them to 29-13 as they fight with the Denver Nuggets for superiority in the Western Conference, though coach Taylor Jenkins acknowledged his team is "not playing perfect basketball."
He was, though, happy to see the Grizzlies "finding different ways to win," adding: "Whether we're playing with a lead or playing from behind. Each game has presented a different challenge for us and our guys have stayed the course.''
Pacers coach Rick Carlisle was clearly impressed by their performance, saying: "[The Grizzlies may] very well may be the best team on the planet right now.''
Taylor is considering selling the team he has owned since 1994 and one of the conditions of the sale is the team must stay in Minnesota.
Garnett, the greatest player in Timberwolves history, said he is part of a group that is a potential buyer.
"No two people love the city more than myself and Glen Taylor and I look forward to trying to work with him to achieve my dream," Garnett wrote on Twitter on Tuesday.
ESPN reported that Vikings owners Zygi and Mark Wilf have emerged as serious candidates to buy the team.
Garnett spent his first 12 NBA seasons with the Timberwolves – winning MVP honours in 2004 – and played for the Boston Celtics and Brooklyn Nets. He returned to the Timberwolves in 2015 and retired the following year.
Garnett is part of a star-studded 2020 NBA Hall of Fame class that also includes Tim Duncan and Kobe Bryant.
The Timberwolves have made just one playoff appearance in the past 16 seasons, with only two winning campaigns during that span. They finished this season 19-45 and were one of eight teams not invited to the NBA's season resumption in Orlando.
Bryant died aged 41 in a helicopter crash alongside his 13-year-old daughter Gianna and seven others in California last month.
The Los Angeles Lakers great, an 18-time All-Star and five-time champion, was one of four first-time finalists named on Friday.
Duncan, the former San Antonio Spurs star with 15 All-Star appearances and five championships, and Garnett – another NBA great – are also finalists.
A four-time Olympic gold medallist with the United States, Tamika Catchings is the other first-time finalist.
Kim Mulkey, Barbara Stevens, Eddie Sutton and Rudy Tomjanovich are previous finalists also up for consideration again.
"When the nominees for the Class of 2020 were announced in December, we knew this class had the potential of being one of the most historic of all time," Naismith Memorial Basketball Hall of Fame chairman Jerry Colangelo said in a statement.
"The untimely passing of Kobe Bryant has left us in a state of reflective mourning and we're proud to honour his legacy while also recognising seven other individuals who have meant so much to our game.
"We congratulate our finalists and those who have supported them on their journeys, and we look forward to revealing the Class of 2020 at the Final Four in Atlanta."
The announcement will take place on April 4.
The Class of 2020 line-up was confirmed by the Naismith Memorial Hall of Fame, with all the finalists announced in February officially named as new inductees.
Bryant, the great Los Angeles Lakers shooting guard, died alongside his 13-year-old daughter Gianna when they and seven others perished in a helicopter crash in California on January 26.
Bryant was 41. He was a five-time NBA champion with the Lakers and an 18-time All-Star, as well as an Olympic champion in 2008 and 2012.
Bryant's Hall of Fame nomination may have been first announced following his death, but his place was a matter of time, and he reportedly was already in line to be inducted this year.
Vanessa Bryant told ESPN: "It's an incredible accomplishment and honour and we're extremely proud of him.
"Obviously we wish he was here with us to celebrate, but it's definitely the peak of his NBA career and every accomplishment he had as an athlete was a stepping stone to being here.
"We're incredibly proud of him and there's some solace in knowing that he was probably going to be part of the 2020 Hall of Fame class."
The Hall of Fame ceremony will take place in Springfield, Massachusetts, on August 29.
Bryant's long-time fellow NBA superstars Tim Duncan and Kevin Garnett also feature in the Class of 2020 - both were 15-time All-Stars in their playing careers - along with college coaching titan Eddie Sutton.
Rudy Tomjanovich, who led the Houston Rockets to two NBA titles, made the grade, together with 10-time WNBA All-Star and four-time Olympic gold medallist Tamika Catchings, trailblazing women's coaches Kim Mulkey and Barbara Stevens, and FIBA executive Patrick Baumann.
Naismith Memorial Basketball Hall of Fame president John L. Doleva said: "The Class of 2020 is undoubtedly one of the most historic of all time and the talent and social influence of these nine honourees is beyond measure.
"In 2020, the basketball community has suffered the unimaginable loss of iconic figures commissioner David Stern and Kobe Bryant, as well as the game itself due to COVID-19.
"We have also banded together like never before in appreciation of the game and those who have made it the uniting force it is today. Today we thank the Class of 2020 for all they have done for the game of basketball and we look forward to celebrating them at Enshrinement in August."
James notched up his 10,000th assist during the second quarter, with a cross-court pass to Carmelo Anthony for an open three.
The Suns were dominant at home to the Lakers, though, putting up 48 points in the first quarter alone on their way to a commanding win.
Having already secured a playoff berth, despite losing at home to the Toronto Raptors on Saturday, Phoenix faced conveniently light work heading into a road back-to-back this week.
Devin Booker continued to shoulder the burden without Chris Paul, putting up 30 points and 10 assists.
With the loss, meanwhile, the Lakers move to 29-38 and teeter dangerously close to touching distance for the San Antonio Spurs and Portland Trailblazers, in the race for the final two Western Conference play-in spots.
Durant leads Nets with Irving in the building
Kevin Durant put up an individual season-high 53 points, including a game-breaking three to give the Brooklyn Nets a 110-107 win over the New York Knicks.
The shorthanded Nets were at least able to have Kyrie Irving in the building for the win, with New York mandates now enabling those unvaccinated for Covid-19 to spectate. However, the mandate still requires the vaccination for people who work there, meaning Irving is still unable to suit up.
At the end of the game, Irving walked off the Barclays Center floor arm-in-arm with Durant, who finished with nine assists and six rebounds to go with the 53 points - one point off his career-high.
Joel Embiid had his 30th 30-point game of the season as the Philadelphia 76ers defeated the Orlando Magic 116-114 in over-time. Embiid finished with 35 points, 16 rebounds and seven assists, while Tobias Harris came up with a crucial late three-pointer to finish with 26 points.
Ja Morant had a quiet game by his standards with 17 points, five rebounds and 10 assists as the Memphis Grizzlies improved to 47-22 with a 125-118 win over the Oklahoma City Thunder.
Doncic dagger propels Mavs to road win
The Dallas Mavericks claimed an impressive win on the road, edging the Boston Celtics 95-92 at the TD Garden. Despite leaving the floor with a hamstring scare in the first half, Luka Doncic’s fingerprints were all over the game’s dying moments - he hit the game-tying three-pointer with 1:21, before being called for fouling Marcus Smart on the potential tying three.
It was overturned on review however, and along with the win, Doncic put up 26 points, eight rebounds and eight assists. On a night where Kevin Garnett's No. 5 jersey was to be retired by the Celtics post-match, the Mavs moved to 42-26 for the year, half a game behind the Western Conference’s fourth-placed Utah Jazz.
