The Celtics reportedly made a significant addition to coach Joe Mazzulla’s staff on Sunday, less than one week after the team’s Game 7 loss in the Eastern Conference finals.

Boston will bring on veteran assistant coach Sam Cassell, according The Athletic’s Shams Charania, joining Mazzulla, who will begin his second season as head coach in 2023. Cassell, 53, has spent the last three seasons as an assistant with the 76ers under recently-fired coach Doc Rivers.

A 19-year NBA veteran and three-time NBA champion, Cassell will return to Boston 15 years after helping the club win a title in 2008. Cassell retired as a Celtic in 2009, and immediately went into coaching, working as an assistant for the Wizards, Clippers and Sixers from ’09 to ’22.

The Celtics’s agreement with Cassell comes just three days after president of basketball operations Brad Stevens vowed to add more experience around Mazulla. Stevens’ comments came on the heels of a report from The Boston Globe’s Gary Washburn regarding the Celtics undergoing major changes within their coaching staff after losing three assistant coaches to new Rockets and former Boston coach Ime Udoka. 

“We’ll look for somebody that has a lot of NBA experience for sure,” Stevens told reporters Thursday when asked about the coaching search.

Mazulla, who was promoted following Udoka’s suspension and eventual ouster, turned in an impressive 2022–23 campaign in his first season at the helm. The 34-year-old led Boston to a 57-25 record, and took the team to its third East finals in four years.