Letting Doc Rivers go to the Los Angeles Clippers was the first sign. Getting rid of Paul Pierce and Kevin Garnett clinched it.

The Boston Celtics are rebuilding.

The Celtics agreed to the terms of a deal that would send the two remaining members of the Big Three that won the 2008 NBA title to the Brooklyn Nets for a package of draft picks and players. Garnett is a future hall of famer, but it’s Pierce’s departure that signals the end of an era for the league’s most-decorated franchise.

“It’s sad to see everybody leave Boston. You just want them to go someplace where they have a chance to win, and they have,” Rivers said at Clippers draft headquarters late Thursday night. “It’s a great trade for Boston, too; not now, later.”

The longest-tenured member of the Celtics, Pierce is the team’s captain, a 10-time All-Star and a likely hall of famer. He is the second-leading scorer in the history of the NBA’s most-decorated franchise, and is also in the team’s top seven in rebounds, assists, steals, games and minutes played.

Garnett is also a future hall of famer, though only the last six years of his career were in Boston. It’s Pierce, who slipped to 10th in the 1998 draft and has been a Celtic ever since, who had a chance to spend his entire career with the franchise and add his name to a list that includes hall of famers Larry Bird, Bill Russell and John Havlicek.

Lakers tell the world

In words and deeds, the Los Angeles Lakers are making it clear how they feel about Dwight Howard. The Lakers took the unusual step earlier this week of putting up billboards around the L.A. area with a photo of the center and the word “Stay.” General Manager Mitch Kupchak also addressed his feelings late Thursday night after the NBA draft.

Said Kupchak: “The message is simple: We care about you and we want you to stay.”

Howard’s impending free agency has been prominent in the Lakers’ minds since their season ended in a first-round playoff sweep.

Howard, a seven-time All-Star, has vowed to make his decision in his own best interests, giving no indication he favored the Lakers over any other team. The free-agency period begins at the end of Sunday night.

Kupchak used the word “optimistic” to describe his feelings about what Howard might do. The Lakers can offer a maximum of $118 million over five seasons, and other teams can offer $88 million over four years.

Around the league

Ray Allen is returning to the Miami Heat next season. He exercised his $3.2 million player option Friday, barely a week after the Heat finished off the San Antonio Spurs to win the NBA Finals. … The Charlotte Bobcats extended a qualifying offer to guard Gerald Henderson, making him a restricted free agent, but not to center Byron Mullens. The qualifying offer of $4.2 million to Henderson will allow the Bobcats to match any offer he receives from another team. The Bobcats decided not to extend Mullens a $3.2 million qualifying offer. He becomes a free agent. … Former New Jersey Nets coach Lawrence Frank will return as an assistant under new coach Jason Kidd. The Nets said they also agreed to terms with assistants Roy Rogers, Eric Hughes and Doug Overton to fill out the staff.