Former NBA champion and All-Star Sam Cassell is joining the Boston Celtics' coaching staff after spending the last few years with the Philadelphia 76ers, according to The Athletic's Shams Charania.

Cassell, 53, is one of the highest-regarded assistants in the league and spent the last three seasons in Philadelphia working under Doc Rivers, who was fired by the organization on May 16.

After losing three key members of his staff to Ime Udoka in Houston, young head coach Joe Mazzulla will now have a veteran coaching presence to lean on next season.

President of Basketball Operations Brad Stevens acknowledged that the organization wanted to add at least one coach to Mazzulla's staff. He wanted it to be someone experienced to help out the 34-year-old, who at times looked overwhelmed in his first season at the helm

"We're going to look for at least one addition to the bench, and he'll lead this charge," Stevens said Thursday after confirming that Mazzulla would be back next year. "We'll look for somebody that has a lot of NBA experience for sure."

And Cassell certainly lives up to that billing.

A three-time champion, he began his coaching career in 2009 with the Washington Wizards and Flip Saunders. He then went to the Clippers with Doc Rivers in 2014 and has been a part of his staffs ever since.

A big plus to adding Cassell is that he has experience with the organization. He was a part of Boston's 2008 championship team, averaging 7.6 points and 2.1 assists in 17 games. It was his final season as a player.