By Matthew Geagan, CBS Boston

BOSTON (CBS) — Al Horford is back in Boston, and the veteran big man couldn’t be happier. He’s eager to take care of some unfinished business with the Celtics.

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That is, of course, raising another banner for a franchise that has plenty of them. Though the Celtics flirted with a trip to the Finals in two of his three seasons, Horford was never able to accomplish that ultimate goal. Now he’s even hungrier for another crack at it in his second go-around in green.

Boston re-acquired Horford in the Kemba Walker trade, after he spent the last two seasons in Philadelphia and Oklahoma City. Horford left Boston in the summer of 2019 for a massive contract from the Philadelphia 76ers, but he quickly found that life isn’t always greener because of a truckload of cash.

Horford wasn’t a fit in Philly next to Joel Embiid, and he spent last season being preserved as trade fodder by the tanking Thunder. Now, he’s eager to play a role in another title run in Boston.

“When this opportunity came up for me, it’s something I’m really grateful for. This is a place I want to be. I’m happy it has been able to work out,” Horford told reporters over Zoom on Thursday. “I appreciate how special of a place that Boston is. For me, being away from it and seeing the type of city that it is, what the team is all about, it’s something that I really missed.

“I feel like I learned a lot, and in my case, change was for the better,” he added. “I’m very grateful to have a second opportunity to be back here and continue to work on what I started here.”

Horford was one of the first big name free agents to sign with the Celtics in their prime — ever — when he signed in the summer of 2016, and he helped the team make it to the back-to-back Eastern Conference Finals in his first two seasons in Boston. While’s he’s now a couple of years older than when he left, he’s confident that he can still play an important role as Boston looks to rebuild its image after a frustrating 2021 season.

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“Five years ago when I had to make a tough decision and leave Atlanta, Danny [Ainge] and Brad [Stevens] sold me on this culture, what we were trying to build in Boston and winning Banner 18. That is something that really excited and motivated me, and something we were really working towards. I think that, obviously, I wasn’t able to get it done when I was with the group,” he said. “Getting an opportunity again to do that, for me it’s looking at what kind of purpose – what can I do to accomplish that. I’m lucky enough to get a second shot to be with this group. It was a good three years for me, but now we get a fresh opportunity.

“It’s a huge challenge; I understand and I know that,” added Horford. “But I embrace that and I look forward to getting to work with the guys that we have.”

Horford says that work has to start now, with guys using the summer to get themselves in the best place both mentally and physically. That will allow them to come together in September ready to go for what should be a normal 2021-22 season.

Horford, now 35, said he is feeling great physically, and is willing to do whatever the Celtics ask of him this season. He’s excited to be reunited with Ime Udoka, who will reportedly become Boston’s new head coach sometime in the near future, whom he worked with during his one season in Philadelphia. He especially loves Udoka’s defensive mind, and thinks he’ll make a great head coach in Boston.

“Ime is a great guy. Him and I had a really good relationship; he was always very professional and his views on the game,” said Horford. “I’m excited for what he brings and how he can help our group. Looking forward to supporting him and getting this thing going.”

Horford is already putting in work at the Celtics’ training facility in Brighton, and he is not alone. He saw Grant Williams and Tacko Fall doing the same, and expects more players to join them over the offseason. And immediately after the news broke that he was returning to Boston, both Jayson Tatum and Robert Williams reached out to him to express their excitement.

Now comes the hard part, but Horford is confident that the team will be able to put a tough season behind them, and focus on the brighter days ahead.

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“We’re going to work really hard to prepare and be excited for the challenge,” he said. “We have a great opportunity in front of us.”