Al Horford’s summer has been anything but a vacation.

First, the five-time All-Star opted out of his contract with the Celtics, a difficult decision given the success he enjoyed during his three seasons in Boston.

Then, Horford signed a four-year, $109 million deal with the 76ers, a move that proved far less difficult given the lucrative offer and the 33-year-old’s excitement over what Philadelphia could accomplish in the Eastern Conference during the 2019-20 campaign and beyond.

“When I decided to opt out, it wasn’t an easy decision,” Horford told reporters Friday during an introductory press conference. “But I did it. I felt like there was going to be a lot of options for me. When June 30 came around, things escalated very, very quickly. There were multiple teams, a lot of strong interest. I had to make what was the best decision for me.

“When (76ers general manager) Elton (Brand) called and spoke with my agent, he laid down this offer. I was very surprised there was such strong interest for me being here. It made the decision very easy, and I’m just excited to be a part of this.”

It wasn’t that shocking when Horford opted out of his contract with Boston, as the presumption was he’d re-sign with the Celtics on a longer deal with a lesser cap hit. Horford had been set to earn $30.1 million in the final year of the four-year, $113 million pact he signed with the C’s before the 2016-17 season.

Clearly, the market for Horford was much stronger than anticipated, though, resulting in his departure. Boston’s loss is Philadelphia’s gain, as Horford will form quite a front-court tandem alongside Sixers center Joel Embiid.

“I think opportunity to play for this type of organization, for this city, was something that I really had to consider and look at,” Horford said. “We’ve got a good group here. I feel really good about our future.”

The Celtics certainly will have a hard time mitigating the loss of Horford, who emerged as a leader both on and off the court. The addition of Enes Kanter should help, as he’ll provide some size and scoring up front, but it’s sure been an interesting offseason for Boston, as the C’s also replaced Kyrie Irving with Kemba Walker amid a chaotic summer for NBA free agency.

Thumbnail photo via Greg M. Cooper/USA TODAY Sports Images