Kyrie Irving’s downfall with the Boston Celtics is well documented.

The mercurial point guard was at the heart of the chemistry issues that plagued Boston’s 2018-19 campaign, and the Celtics’ turnaround so far this season has been largely attributed to Irving’s departure and the arrival of his highly regarded replacement, Kemba Walker.

Some, including Danny Ainge and Marcus Smart, have been quick to point out that last season’s underwhelming results weren’t Irving’s fault. But it’s fairly obvious the six-time All-Star’s attitude proved detrimental to the Celtics’ quest to establish themselves as legitimate NBA Finals contenders.

Here’s what The Athletic’s Jay King wrote in a piece published Tuesday:

He would go through stretches, sources said, where he just shut off. One assistant coach said he once rode about 30 or 40 flights on an elevator with Irving — and the guard did not say a single word. By February, the organization had realized how much Irving’s mindset could impact the rest of the team.

The book officially closed on Irving’s tenure with the Celtics when he signed with the Brooklyn Nets in free agency over the summer despite announcing before the 2018-19 season that he intended to re-sign with Boston. It sounds like Irving might have checked out well before that point, though, even behaving strangely after the Celtics defeated the Milwaukee Bucks 112-90 in Game 1 of the teams’ Eastern Conference semifinals series.

Here’s more from King:

While Celtics teammates worked out on the floor the next day, sources say Irving climbed into the stands and sat by himself. The practice was voluntary, but the way he disengaged himself — while his teammates put in work — struck observers.

“He was just disconnected,” said one witness.

None of this should come as a surprise to those who have followed Irving, who wound up in Boston before the 2017-18 season after requesting a trade from the Cleveland Cavaliers. But the Celtics sure seem like they’re in a better place now — from a camaraderie standpoint, at least — than they ever were with Irving in the mix.

“Night and day,” a team source told King of Irving’s exit and Walker’s entrance.

Irving was supposed to return to Boston and face the Celtics on Wednesday for the first time since joining the Nets. Unfortunately, he’ll be sidelined for the much-anticipated, pre-Thanksgiving showdown at TD Garden while dealing with a shoulder injury.

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