Undefeated boxing champ Floyd Mayweather is reportedly $6.5 million richer after placing his bet on the Miami Heat which won the eastern conference finals play off against the Indiana Pacers on June 3.

Floyd 'money' Mayweather is said to have wagered a staggering $5.9 million bet on Lebron James and company, which saw the boxer walking away with $6.5 million more after the game.

It was the Vegas Gambling Steam who cracked the news of the champ's whopping bet on Twitter.

"Good source from my #HeavyHitters Vegas crew alerted me that Floyd Mayweather has laid over $5,900,000 on Heat -7 tonight in Vegas," the VGS tweeted.

Benjamin Lee Eckstein of AmericasLine.com, a nationally syndicated odds column, spoke to New York Daily News and said he found the betting "ridiculous."

"I know that there have been people who walked into a casino and bet a million dollars, but not on basketball. It was always the Super Bowl," he said.

Due to the huge amount of his bet, Mayweather apparently had to apportion the money across nine sports books.

"I don't think that anybody's taking a six million dollar bet at one shot," Eckstein said. "You'd probably have to call (Vegas mogul) Steve Wynn personally for that."

The gamble paid off for the highest-paid athlete in the world. Even prior to the game, the team of Lebron and Dwayne Wade was already winning the odds with a 7-point favourite versus the Pacers. The Heat ended up toppling their opponents 99-76.

Reports say that Mayweather wagered the huge amount after sealing a six-fight deal worth $200 million with Showtime. His next fight is scheduled for September 2013 with Canelo Alvarez. The fight is said to give him at least $40 million.

The boxing star does not keep it a secret that he loves the betting game. OnTwitter, he usually shares his winning and losing tickets to his followers. But the boxer has yet to tweet about his latest big win.

According to Grandland.com, Mayweather has profited $3,938,722 from all his placed bets from August 2010 to February 2012. The boxer apparently has had a spotless run as shown by the photos he tweeted of his 46 betting slips.

Meanwhile, also spotted watching the Heat vs. Pacers game in Miami were celebrities Justin Bieber and David Beckham.