Celtics guard Marcus Smart celebrates after Boston beat the Miami Heat 104-103 in Game 6 of the Eastern Conference finals last month in Miami. AP file photo

BOSTON — Shortly after midnight Thursday morning, after making undoubtedly the most difficult decision in his short time as the Boston Celtics’ president of basketball operations, Brad Stevens had to make the similarly difficult phone call.

Marcus Smart, of course, was on the other line.

Stevens, of course, had to deliver the news to the heart and soul of the Celtics, the beloved point guard he coached for seven seasons and has developed a close bond for nearly a decade, that he was being unexpectedly traded.

“It was hard,” Stevens said, stating the obvious early Friday morning at the Auerbach Center, about 24 hours after sending shockwaves through Boston.

The trade was officially announced at 1:59 a.m. Friday morning, after the draft, trade calls and the final details were completed. It brings Kristaps Porzingis to Boston, where the skilled big man will give the Celtics a brand new look in their pursuit of a championship. It sends Smart to Memphis, where he’ll assume a leadership role on a young, contending Grizzlies squad.

It also sends out a fabric of the Celtics’ identity for the last nine years. The backbone and the glue of this franchise as it rebuilt into a championship contender. It’s hard to put into words what Smart’s importance was. On that shocking phone call, Stevens did his best, but made it brief.

“You can imagine it wasn’t very long,” Stevens said. “It was just your best chance to share your gratitude to him. …

“I think that because of these things and the sensitivity of these things and how many people talk about them and the wild speculation when something happens, it’s hard to digest, it’s hard to process.”

On Thursday morning, as he tried to process the emotions and feelings that were certainly still raw and fresh, Smart paid a visit to the Auerbach Center. It was a chance for Stevens and whoever else was in the building to see him again before he departed, to have a proper farewell to a person that meant so much to the organization.

It was only right, only fitting. Smart was the sixth pick of the 2014 draft shortly after the Celtics finished a 25-57 season, which was the first after Paul Pierce and Kevin Garnett were traded. Smart was the first big piece as the Celtics began a new era. He left them as championship contenders. In between, he created a legacy that will not be forgotten in Boston.

“The greatest legacy you can leave is to be someplace and it’s better off because you were there,” Stevens said. “And I think that everybody here feels that way. I think that he will always be appreciated and thought of so fondly here for any number of reasons. Obviously everybody loved the way he plays and how hard he plays, but also his work in the community.

“We’re all really grateful to have had Marcus in our life for as long as we’ve had and are sad to see him go but know that he’s gonna have a huge impact on a really good Memphis team. So very difficult, very difficult conversations, really hard to do. But he’ll always have Boston for sure, right? I think Boston really appreciates him, and certainly I do, and he knows we’ll do anything for him.”