The Boston Celtics have their star. Ken Berger of CBS Sports reports that free agent Al Horford agreed to a four-year, $113 million deal with the Celtics on Saturday. With the move, Boston not only secures an All-Star center, but possibly moves into pole position for Kevin Durant, who is expected to make his decision Monday.

The Atlanta Hawks had maintained their intention to retain Horford, but were reportedly unwilling to give Horford the full max. This presumably means they will not be trading Paul Millsap as it had been reported they were considering. Horford confirmed the decision on Twitter.

The move is a major score for the Celtics, who were in search of a star-caliber player, while the Hawks who lose arguably their best player. Here are five things to know from a big move that may still have even bigger ripple effects with Kevin Durant still out there.

1. Horford's perfect for Boston

He's a smart-passing, smooth-touch big man who can finish inside, shoot from the perimeter, set great screens and play great defense. He complements nearly any player, but especially Isaiah Thomas with his combination of size and savvy.

Horford can hurt teams with the pick and pop, exploit rotations to Thomas or the other Celtics' guards with short dunk cuts, spot up baseline, or score in the post. He is the most versatile big man on the market by far and one of the most versatile bigs in the league.

He's also a proven winner. He won two titles in college, he's made the playoffs every season with the Hawks. He's a veteran who doesn't need his name on the side of buildings or banners, who goes to work, and is a highly intelligent player. He's set to make the Celtics better in every regard.

2. The KD angle is very real

There have been consistent whispers that the Thunder were trying to pursue Horford because of Durant's interest in him. The same can be said for the Warriors, and the Heat. Durant met with the Celtics Saturday night (with Tom Brady in attendance) and Boston can now offer a roster with Isaiah Thomas and Al Horford along with a bevy of good players in a historic sports town with a grand tradition.

If the Warriors and Thunder were thought to be in the lead for Durant, the Celtics rolled on up to the front of the line by landing Horford, a veteran star who can compliment KD.

3. Celtics may not be done

With Jared Sullinger (restricted free agent), Amir Johnson, Tyler Zeller (restricted free agent) and Kelly Olynyk, and the fact that Jae Crowder often plays small-ball power forward, there's a crunch in the front court. Boston is likely to try and clear space by letting Zeller and Sullinger go. Olynyk and Johnson are interesting in that both can play next to Horford, but Horford is also, obviously, better than both of them and can thus simply replace them. If the Celtics land Durant, they may clear those guys out to create cap space, and if they don't, they may look to swing for another star in trades.

Olynyk proved himself to be a plus defender last year and is one of their best shooters from range. You can play Horford at power forward and Olynyk at stretch five and have size, defense and shooting all over in that lineup.

Either way, the Celtics have options.

4. Disaster for the Hawks

The Hawks effectively swapped Al Horford for Dwight Howard, which is a great move in 2010 but a horrible one in 2016. Howard has had multiple surgeries on his back and knees, and has never been the kind of efficient player Horford is. Yes, in his prime he was better and yes, he still provides a level of rim protection and rebounding that Horford doesn't. But this is a downgrade. Howard is nowhere near the offensive threat that Horford is, and Horford may be the better overall defender. The Hawks got worse on Saturday, and reportedly they did it to save about $6 million.

Ultimately, Atlanta was either going to lose Paul Millsap, its best player, or Horford, so it makes sense to choose Millsap over Horford, but the reality is that Millsap and Horford in tandem were better than Horford and Howard would have been or that Millsap and Howard presumably will be. They had a team that went to the Eastern Conference finals after winning 62 games in 2015, then returned to the playoffs as a four-seed last year. Were they well behind the Cavaliers? Absolutely, and a bad matchup to boot. But they're further away now. All they really did in getting Howard and losing Horford is pay a lot of money for worse parts.

5. The East has changed

Boston is, before Durant's decision, probably slightly behind the Toronto Raptors for second-best team in the East, but could very easily wind up in the No. 2 seed next season. This puts the Celtics ahead of Atlanta and Miami by adding the kind of do-it-all player they did not have last season. There are likely more changes coming for Boston, but this alters the East. If Horford's decision winds up swinging Durant to the Eastern Conference, be it in Boston or Miami, it's going to radically alter the title picture in the NBA.

Al Horford Hawks
Al Horford is headed to the Celtics. USATSI