Floyd Mayweather vs. Conor McGregor mega-millions bout set for Aug. 26

Floyd Mayweather Jr. will come out of retirement to meet UFC star Conor McGregor in an Aug. 26 boxing match that will feature two of the top fighters in the world.

The two fighters both announced the fight Wednesday, after months of speculation about whether Mayweather would be lured back to the ring at the age of 40 to face a mixed martial arts fighter who has never had a pro boxing fight.

Oddsmakers immediately made Mayweather an 11-1 favourite in a fight that will take place in a boxing ring and be governed by boxing rules. It will be contested at 154 pounds.

"It's official," Mayweather said on Instagram next to a video poster of both fighters.

"THE FIGHT IS ON," McGregor tweeted several minutes earlier, posting a picture of himself next to one of Mayweather's father, Floyd Sr., a dig at the boxer's age.

Mayweather, who retired in September 2015 after winning all 49 of his pro fights, will face the Irish UFC superstar at the T-Mobile arena on the Las Vegas Strip. He had tweeted a picture of himself sparring in recent days to show he was getting ready for the bout.

"This is really an unprecedented event," said Stephen Espinoza, who heads Showtime Sports, which will handle the pay-per-view. "Really we haven't seen anything in modern history that resembles it, it's impossible to predict how many sales this will do."

Espinoza said the fight came together quickly after McGregor and the UFC reached agreement last month on their end of the deal and Mayweather's team pushed for the fight in recent days.

"All parties were motivated and reasonable and thrilled we could get everything done," he said. "The sky's the limit on this."

McGregor, the wildly popular UFC star, is 21-3 in UFC fights, and is coming off a win in November against Eddie Alvarez in which he became the UFC's first two-division champion. Though he hasn't boxed professionally, McGregor did box while growing up and is known for his striking expertise in UFC.

"The impossible deal is now happening," UFC chief Dana White said on ESPN.

Mayweather heavily favoured

The two fighters are expected to do a press tour shortly before going into final training for the fight. The cost of tickets and the price of the pay-per-view has not been decided, though the pay-per-view is expected to be at or near the $99.95 US charged for Mayweather's 2015 fight with Manny Pacquiao that drew a record 4.4 million pay-per-view buys.

Mayweather will come off a two-year retirement in a bout that McGregor has been pushing for nearly that long. Nevada boxing officials on Wednesday approved the date for a Mayweather Promotions bout.

Mayweather last fought in September 2015, beating Andre Berto and then announcing his retirement. His fight before that, a decision win over Pacquiao, was the richest in boxing history and reportedly made him more than $200 million US.

Though oddsmakers make Mayweather a big favourite, the thought of the fight has excited many in the MMA world. It has also intrigued some in boxing, though most dismiss McGregor's chances under boxing rules against one of the greatest defensive fighters in history.

Oddsmaker Nick Bogdanovich, who set the 11-1 line at the William Hill chain of sports books, said the odds would be even more lopsided if it wasn't for the deluge of small bets expected to come in from UFC fans on their fighter.

"Realistically if we were just putting up a number and didn't have to take bets on it, Floyd would be 100-1," Bogdanovich said. "But this will be a very, very big betting fight for sure, one of the biggest ever."

Adding to McGregor's challenge, the fighters will be using 10-ounce boxing gloves instead of the smaller UFC gloves, and he will not be allowed to use the leg kicks or takedowns that are part of mixed martial arts.

Even if the actual bout may not shape up as a great match, the run-up to the fight will. Both fighters are noted for their ability to sell their fights, and both have engaged in trash talking and more to promote their bouts.

"As with every Mayweather and McGregor fight, part of the appeal is the spectacle and outsize personalities who are participating in it," Espinoza said. The pay-per-view revenue for the event would likely gross tens of millions of dollars.

It comes less than a month before Gennady Golovkin and Canelo Alvarez meet in a highly anticipated fight Sept. 16 that could rival it for pay-per-view buys.