BOSTON — The Boston Celtics heard loud and clear what everyone was saying about them before this season.

They heard all the predictions about how they would take a step back from the NBA’s top tier, with Jayson Tatum rehabbing from the ruptured Achilles tendon he suffered in the playoffs last May.

They heard the narrative that this would be a throwaway year, likely ending with Boston in the draft lottery, after an offseason shakeup that included the departures of key 2024 championship contributors Jrue Holiday, Kristaps Porzingis and Al Horford.

So when the Celtics last month notched their 50th win for the fifth consecutive season, Jaylen Brown didn’t hold back in ripping that narrative into confetti.

“50 wins in a gap year,” Brown posted on X, with a shamrock emoji.

Enough said.

Now, as the Celtics prepare for their 12th straight playoff appearance overall and fourth under coach Joe Mazzulla, they are whole again following Tatum’s return last month. And the rest of the NBA is acknowledging what the Celtics have believed for some time: The sky remains the limit for this team, which is the No. 2 seed in the Eastern Conference.

Brown, who seized the leadership reins during an MVP-caliber season, acknowledged that he was surprised “a little” about just how well the cards have fallen for this group.

“Obviously, my mentality was come in and compete. But the way the group merged together as quickly as it did — it didn’t take us long. I thought it would take us a little longer,” Brown said. “We were trending upward post-All-Star break, but we kind of figured it out maybe the first 10 or 15 games. We started clicking and jelling. That just doesn’t happen.”

With Tatum sidelined for the first 65 games, Brown flourished as the No. 1 option and leader, taking his game to new levels on both offense and defense. He posted career-high averages in points (28.7), rebounds (6.9) and assists (5.1).

He also got lots of support.

Derrick White struggled offensively at times but remained a stalwart on defense, leading NBA guards in contested shots (550) while ranking second among guards in blocks per game (1.3).

Payton Pritchard adjusted his game, first as a starter and then by returning to the bench role that earned him Sixth Man of the Year last season. Sam Hauser remained a reliable threat from the 3-point line, and center Neemias Queta’s game grew in leaps in his first year as a starter.

There were some questions about how Tatum’s return March 6 would affect the flow of a group that learned to adjust and thrive without the six-time All-Star.

Instead, Tatum reacclimated himself in short order, averaging 21.8 points, 10 rebounds and 5.1 assists in 16 games.

“Quite honestly, I think it’s impressive that he’s gotten back to the level that he’s at as fast as he’s done it, while also keeping the main thing the main thing, which is remaining healthy and giving us the best chance to win every night,” Mazzulla said. “It’s a credit to him.”

One of the final hurdles to Tatum feeling “back” came April 9 when the Celtics visited the New York Knicks in his first game at Madison Square Garden since suffering his injury. He said the past month strengthened a love for basketball that he feared during rehab he might lose.

“You go through ups and downs mentally when you go through an injury, especially the one that I had,” Tatum said. “Moments of doubt or things like that. But there’s definitely a sense of gratitude.”

For Brown, it’s also put into perspective just how unlikely his nine seasons playing alongside Tatum have been.

Bill Russell and Bob Cousy played together for seven seasons for the Celtucs, and Shaquille O’Neal and Kobe Bryant played together for eight with the Lakers.

“I think it’s been a historic run. We were able to deliver a championship in 2024. Unfortunately we had opportunities in the past that got away from us, but we’ve been right there for a long amount of time. We’ve gained a lot of experience,” Brown said.

“Everything isn’t always perfect but it’s not supposed to be. It’s a part of the journey. … I’m excited to go have another opportunity.”

Brown has an eye on bringing more trophies to Boston.

“I’m still improving. I’m still getting better. I’m still learning. I’m still growing,” he said. “I feel like I’m entering my prime, and I’m excited to maximize my potential and then take advantage of every opportunity I have to win and just be a part of a team, and be a part of something special.”