It's not just a rumor anymore. This time it's straight from the mouth of King James himself: "This fall, I'm going to take my talents to South Beach and join the Miami Heat."

LeBron James made the announcement during a live primetime television special on ESPN this evening.

"I don't have any doubts at all," he told ESPN's Jim Gray. "I've slept enough, or the lack of sleep."

James' announcement was met by euphoria from fans in Miami and anger in Cleveland, where the superstar spent his first seven NBA seasons after high school stardom in nearby Akron, Ohio.

James said he informed the Heat of his decision only moments before his appearance on the 9 p.m. ET ESPN special, that he had not given advance word to the other teams bidding for his services, and that the number of people who knew of his decision in advance could be counted on the fingers of one hand.

"I feel like this is going to give me the best opportunity to win and to win for multiple years," James said, explaining why he will join fellow free agents Dwyane Wade and Chris Bosh in Miami. "I want to be able to win championships."

Watch James elaborate further on his decision to join the Miami Heat during an exclusive interview with Robin Roberts on ABC News' "Good Morning America" at 7 a.m. ET Friday.

After the announcement, ESPN commentator Michael Wilbon asked James to react to footage of fans in Cleveland burning a James jersey.

"I can't get involved in that," James said. "One thing I didn't want to do was make an emotional decision. I wanted to do what was best for LeBron James and what LeBron James was going to do to make him happy. ... This is a business, and I had seven great years in Cleveland."

Later, he admitted, "To the fans of Cleveland, the times that we had were like no other. ... I feel awful that I'm leaving. I feel even worse that I wasn't able to bring an NBA championship to that city."

James' words were little consolation to the Cleveland Cavaliers and their fans.

"He's one of our own," said one angry fan outside the Hairy Buffalo Bar in Lakewood, Ohio, according to ABC Radio. "He's from Akron. He has a tattoo of loyalty on his body, and he ignored that to go chase a championship with Chris Bosh in Miami."

In an open letter to his team's supporters, Cleveland Cavaliers majority owner Dan Gilbert declared that "our former hero" had committed "cowardly betrayal" against his hometown, and vowed in boldfaced capital letters: "I PERSONALLY GUARANTEE THAT THE CLEVELAND CAVALIERS WILL WIN AN NBA CHAMPIONSHIP BEFORE THE SELF-TITLED FORMER 'KING' WINS ONE."

Miami Heat president Pat Riley and Wade posted far more ecstatic messages on that team's website.

"We are thrilled that LeBron James and Chris Bosh have decided to come to Miami to join forces with our truly great player, Dwyane Wade," Riley said. "We are looking forward to the opportunity of building something that our fans in Miami will be proud of for a long, long time. The journey is just beginning."

The LeBron Watch

For days, commentators have been following every hint on where the free-agent forward might land, a decision that was seen to mean millions more dollars in profits and vastly improved on-the-court fortunes for whatever team he picked.

A prediction by ESPN's Chris Broussard early Thursday that James would join Wade and Bosh to sign with the Miami Heat caused shares of the New York Knicks' parent company, Madison Square Garden Incorporated, to drop.

The stock had gone up after it was announced James would air his decision live on ESPN from the Boys & Girls Club in Greenwich, Connecticut, not far from New York City. The broadcast benefitted The Boys & Girls Clubs of America.

"It just shows you how front and center this two-year odyssey of where he's going to go has become," Brad Adgate, a media analyst at Horizon Media, told ABC News Radio.

The Cleveland Cavaliers tried to retain James' talents and offered the lure of continuing to play for his hometown team.

Betty White, star of the sitcom "Hot in Cleveland," taped public appeals for James to stay at home, and members of the media have noted James' departure likely would be an economic jolt to the Cavaliers and the city of Cleveland, where he has been a huge draw.

But representatives of teams in larger markets also courted James with a barrage of big-city glitz.

The New Jersey Nets brought rap superstar Jay-Z, a minority partner with the team, and Mikhail Prokhorov, the team's principal owner who is one of the world's richest men -- and the suggestion of an international marketing push behind James.

The New York Knicks suggested James picture his name in big-city lights alongside a superstar or two to be named later, and Mayor Michael Bloomberg made a personal appeal for James to come to New York.

The Chicago Bulls, the team where Michael Jordan starred, also came calling.

The Heat brought Riley, a legendary and charismatic former coach, to the table, and then the prospect of playing alongside Wade and Bosh.

'No Leaks' Before LeBron's Decision Day

Through it all, James' inner circle was able to keep his decision under wraps until the end -- though he didn't do it without being coy.

Earlier in the day Thursday, James invited his followers on Twitter (@KingJames) to submit questions in advance about his announcement along with the tag #lebrondecision. (The invitation proved irresitable to jokers like @kenrwhittaker, who replied "Apple is releasing a special edition @kingjames iPhone. Problem is, it only vibrates b/c it doesn't have a RING".)

One wag even started Tweeting as James' ego (@LeBronJamesEgo). One typical tweet reads: "CHECK IT - I'M NOT ALWAYS BOUT ME I'M GONNA SAVE ONE ANIMAL FROM THE BP OIL SPILL AND NAME IT LEBRON JR. WHO WILL BE THE LUCKY SEA TURTLE???"

Yet through it all, the selection remained a secret.

"There've been no leaks," said Will Leitch, founder of the sports web site and a contributing editor for New York magazine. "Every 'leak' has been contradicted by another 'leak' moments later."

If the goal of speculation, analysis, reading of tea leaves and finally, a prime time special, is to maximize attention, Adgate, of Horizon Media, said it has worked for James.

"He's become bigger than the sport," Adgate said. "He thought he could pull this off and he's doing it."

Adgate believes James is as clever as another famous person who is her own brand.

"What Oprah Winfrey has done for talk shows and being a savvy mainstream personality, Lebron James is doing the same thing with sports," he said.

Adgate expected 20 million people to watch James' primetime announcement, more than watched the NBA finals.

ABC News' Aaron Katersky, Brian Braiker, Karen Travers, Brian Cohen and Lee Ferran contributed to this report.