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UPDATE: Friday, July 6 at 10:16 p.m. ET by Austin Green

Ray Allen has reportedly agreed to sign with the Miami Heat, according to Heat owner Micky Arison via Twitter:

Its 2:30am in London and I was just woken up with great news.Welcome to the family #20!! — Micky Arison (@MickyArison) July 7, 2012

Allen's agent Jim Tanner confirmed the news, according to Brian Windhorst of ESPN.

Ray Allen has agreed to sign with the Heat, agent Jim Tanner said. Heat owner @MickyArison broke the news. — Brian Windhorst (@WindhorstESPN) July 7, 2012

This is a fascinating development, as the NBA's all-time leading three-point shooter will be ditching his former teammates in Boston to join their hated rivals.

There are many possible reasons why Allen chose Miami: the sun, an increased role, another opportunity to win a championship. As Adrian Wojnarowski of Yahoo! Sports reports, though, those weren't Allen's only reasons for taking his talents to South Beach.

The deterioration of Ray Allen's relationship with Rajon Rondo played a significant factor in his leaving for Miami, several sources tell Y! — Adrian Wojnarowski (@WojYahooNBA) July 7, 2012

This is a serious blow to the Celtics, as the two-time defending Eastern Conference champs will be even stronger next season. With Allen spacing the floor for LeBron James, Dwyane Wade and Chris Bosh, the Heat's offense will be even scarier than when they won the NBA title last month.

Allen is a career 40 percent shooter from beyond the arc, and if he can stay healthy next season, the rest of the league is in trouble.

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Ray Allen has left Miami without a contract.

According to Brian Windhorst of ESPN.com, Allen met with Heat officials in Miami for the majority of Thursday, but left on Friday without signing his name on the dotted line. Windhorst's sources said Allen can't decide if he should join the Heat or return to Boston, where he has played since 2007:

The sources did not go into specifics, saying Allen is torn because remaining a Celtic is still very much an option.

Windhorst went on to add that the most Miami could give Allen is a three-year, $9.5 million deal to play alongside LeBron James, Dwyane Wade and Chris Bosh. The defending champs have assured Allen extensive playing time.

The Celtics can toss a two-year, $12 million contract in his direction. Despite signing Jason Terry, the organization believes both players can co-exist and play together at the same time. It would certainly give the Celtics a ton of depth at the shooting-guard position.

Boston can also provide him with a no-trade clause, according to the Boston Herald—something Miami can’t do.

The Minnesota Timberwolves are considered a sleeper candidate for Allen, but they would have to blow him away with their offer to sway Allen away from the Eastern Conference.

With Kevin Garnett re-signed, a return to Boston would mark one last push for the Big Three to win a title. While Allen may not owe it to the Celtics organization to stay loyal, considering he was openly shopped for much of last season, it will be incredibly difficult for Allen to ever look Garnett and Paul Pierce in the eye again and explain his decision to join their rival.

Ethan Skolnick of The Palm Beach Post sums it up nicely:

If you've ever considered leaving a job where you liked a lot of people and you've had some success, u get why this is not easy for Allen. — Ethan J. Skolnick (@EthanJSkolnick) July 6, 2012

Will the additional cash and no-trade clause be enough to convince Allen to stay in the Northeast?

Friday’s developments certainly suggest as much.