It's a done deal. Former pound-for-pound king Floyd Mayweather will come out of retirement to face UFC lightweight champion Conor McGregor in a boxing match on Aug. 26 that could challenge Mayweather's financial and pay-per-view records.

Mayweather (49-0, 26 KOs) formally made the announcement Wednesday on social media, 73 days before the bout will take place in Las Vegas. The event, televised by Showtime pay-per-view and promoted by Mayweather Promotions, is expected to be held at either the MGM Grand or T-Mobile Arena.

Two years removed from his last bout, a September 2015 decision win over Andre Berto, the 40-year-old Mayweather will face the 28-year-old mixed martial artist McGregor, in a carnival fight of sorts considering the UFC lightweight champion has never had a boxing match as an amateur or professional. Still, worldwide interest is expected because of the brash personalities involved and the nearly two-year build of trash talk. 

The fact that the fight even came off is a bit surprising considering McGregor (21-3 MMA, 18 KOs) is under contract with UFC. Company president Dana White was initially against the idea, warning McGregor it would be an "epic fall" if he pursued the fight, but eventually came around earlier this year.

Moments before Mayweather announced the fight on Wednesday, McGregor threw his own first punch by tweeting out a picture of himself and Floyd Mayweather Sr., the former boxing champion's father. 

White said the bout will take place at the super welterweight limit of 154 pounds with 10-ounce gloves and at the T-Mobile Arena. Mayweather has fought as high as 154 pounds on three occasions, defeating De La Hoya, Miguel Cotto and Canelo Alvarez in world title bouts.

McGregor has fought as high as 170 pounds in MMA but won his first UFC title at featherweight (145) in 2015. Last November, he knocked out 155-pound champion Eddie Alvarez to become the UFC's first simultaneous two-division champion. (He then gave up the featherweight belt.)

Despite the fanfare that's expected for this combat sports spectacle -- experts predict the fighters will combine to earn more than $175 million -- there's little evidence to suggest McGregor has anything more than a puncher's chance.

The choice of opponent is curious for Mayweather, outside of the obvious financial incentives, considering a victory would improve his record to 50-0, one fight better than former heavyweight champion Rocky Marciano's revered mark for a fighter who retired as champion.

Both Mayweather and McGregor have consistently broken PPV records in their respective sports.

In 2015, Mayweather set a new PPV mark in combat sports by teaming with Manny Pacquiao to sell 4.6 million buys for their superfight, which took more than five years to build. The fight nearly doubled Mayweather's previous record of 2.4 million against Oscar De La Hoya in 2007.

While no single UFC card has yet to reach two million buys -- a mark reached three times in boxing, each time with Mayweather in the marquee -- McGregor owns three of the top five and remains the biggest draw in his respective sport.

Neither Mayweather Promotions, UFC nor Showtime has made an official announcement at this time.