Gordon Hayward has agreed a four-year, $120m (£90.3m) deal to join the Charlotte Hornets, according to ESPN.
The monster deal punctuates a busy week for Charlotte, who drafted point guard LaMelo Ball at No 3 overall earlier in the week.
The Athletic reported that Hayward's deal is fully guaranteed.
Charlotte are coming off a 23-42 campaign and have missed the playoffs for four straight seasons.
Hayward enjoyed a bounce-back season last year, in which he averaged 17.5 points, 6.7 rebounds and 4.1 assists in 52 games (all starts) with the Boston Celtics.
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He has averaged 15.3 points, 4.4 rebounds and 3.5 assists across his 10-year career, which included seven seasons with the Utah Jazz and the last three seasons with the Celtics.
In Hayward's first game with Boston, he sustained a gruesome leg injury that cost him the rest of the season. He averaged 11.5 points in a mostly reserve role upon his return in 2018-19 before returning to the starting lineup last season.
Several teams, including Hayward's home state Indiana Pacers, were interested in adding him before Charlotte sealed the deal.