Former multi-division boxing world champion Floyd Mayweather has announced he will fight UFC lightweight champion Conor McGregor in Las Vegas on August 26.
The high-profile duo both took to Twitter on Wednesday evening to confirm their eagerly-awaited showdown.
The fight will take place under normal boxing rules, despite McGregor having never boxed as an amateur or on the professional circuit.
The 40-year-old Mayweather is unbeaten as a professional boxer and announced his retirement after winning his 49th consecutive bout against Andre Berto in September 2015.
Mayweather said "it's official" on his Instagram account next to a picture of both fighters while McGregor had tweeted "THE FIGHT IS ON" several minutes earlier, cheekily posting a picture of himself next to a photo of Mayweather's father, Floyd Sr.
The 28-year-old McGregor has been pushing for the fight for some time and it came together this week, with Nevada boxing officials approving the date on Wednesday.
Promoter Dana White told American sports broadcaster ESPN the fight will be contested at 154lbs, will take place at the T-Mobile Arena and the pair will wear 10-ounce boxing gloves.
Mayweather has been installed as a heavy favourite by Las Vegas oddsmakers and many pundits dismiss McGregor's chances under boxing rules against one of the greatest defensive fighters.
However, the bout is sure to generate enormous interest and Mayweather will reportedly be paid over $100m US for the contest.
McGregor has become one of the most recognisable mixed martial artists in the world since he won the UFC featherweight title in December 2015.
After splitting two high-profile bouts with Nate Diaz, McGregor knocked out Eddie Alvarez to add the organisation's lightweight title in December last year.
He and McGregor first mooted the idea of a fight in a series of exchanges on social media, in which the Irishman urged Mayweather to step up and sign.
The fight will draw comparisons with the 15-round draw Muhammad Ali fought against Japanese professional wrestler Antonio Inoki in Tokyo in 1976, in which each man was allowed to use his own respective talent.
"Conor McGregor is a massive star in MMA and UFC but has never gone inside a boxing ring before.
"But, there is the element of the unknown. Floyd Mayweather is 40 now and has been out of the ring for two years.
"People are asking, 'If Conor can hit him with his powerful left hand, will Mayweather be able to survive that?'."
White, in whose organisation Irishman McGregor has become a world champion, told Fox Sports: "It's definitely the biggest fight ever in combat sports history, and probably going to be the biggest payday ever.
"Let's just put it this way - all sides involved are pretty happy with their deals!"