But few were as happy as Dave Blatt, who took over as the Cavaliers coach three weeks ago and will make his NBA debut the same night James plays his first game for Cleveland since 2010.
"I'm thrilled with the news," Blatt said on Friday. "It's exciting for the team, the state and basketball. Life is full of surprises."
Blatt coached Russia to a bronze medal at the 2012 London Olympics and Maccabi Tel Aviv to this year's Euroleague crown, but will head a young NBA squad that includes guard Kyrie Irving and Andrew Wiggins, who was the top pick in last month's NBA Draft.
"Welcome back bro. Your city awaits you," tweeted Cavaliers forward Tristan Thompson.
Fan love flowed in the same city where Cavaliers fans burned James jerseys four years ago, crowds cheering and holding signs in support of James near the team's home arena.
Fresh Brewed Tees, a T-shirt maker, sold out of a truck full of shirts with the logo "FOR6IVEN: The Kingdom Restored," the 6 in place of the letter "G" standing for James' jersey number.
A photo of James in a Cavaliers number 6 jersey hints that he will leave his Miami number behind in Florida.
Heat president Pat Riley expressed "disappointment" but said James' desire to play in his hometown should be respected.
"While I am disappointed by LeBron's decision to leave Miami, no one can fault another person for wanting to return home," Riley said.
"The last four years have been an incredible run for south Florida, Heat fans, our organization and for all of the players who were a part of it. LeBron is a fantastic leader, athlete, teammate and person, and we are all sorry to see him go."
Heat owner Micky Arison sounded a sad note for his team, although he thanked James and later the team tweeted: "Thanks for the memories."
Cleveland's "Return of the King" sparked comments from beyond basketball.
US World Cup forward Jozy Altidore tweeted, "Can't blame a man for wanting to return home to play. Wish nothing but the best to KingJames!!"
Retired US tennis star Andy Roddick, a Heat fan, poured out his shock onto Twitter.
Roddick was especially miffed at how James had forgiven Cavaliers owner Dan Gilbert, who had called James a coward in an open letter after his departure four years ago.
"Lebron is a bigger man than me.I would have had a hard time forgiving Gilbert after that letter. Props to Lebron," Roddick tweeted.
"I'm a Heat fan and I'm not even a little upset w Lebron. Cavs fans please save me the 'how about giving us some credit for forgiving him?'"
Among the homemade Twitter tributes was an altered movie poster for "Lord of the Rings: The Return of the King," with James' face.
And even pop star Justin Bieber got involved, tweeting: "Good luck @KingJames #Cleveland"