Gennady Golovkin will face Kell Brook on September 10 at the O2 Arena for the unified Middleweight World Championship.
Current IBF welterweight champion Brook will jump two divisions to take on the current WBA Super, WBC and IBF world middleweight champion in a decision that has stunned the world of boxing.
Brook will retain his status as IBF welterweight champion and will take a record of 36 wins from his 36 professional fights into the bout later this year.
"This is the fight and the moment I have been waiting for for some time. We've tried and tried to lure the best to come and fight me and now we've got the best of the best - the No 1 fighter in the world is coming to the UK," Brook told Sky Sports News.
"When this fight got offered to me I accepted within minutes and I can't wait. Everyone knows I'm a huge welterweight and I know I will carry my speed and accuracy and even more power through the weights.
"This is the ultimate fight, one of the biggest international fights the country has seen in many years - you have seen some huge names run from GGG but I'm running to him. I'm a 'Special' fighter and I will show the world on September 10."
Brook's promoter Eddie Hearn added: "I cannot tell you how excited I am for this mega fight. I couldn't be happier for Kell. We have pushed for that big name for a long time with many reluctant to step into the ring with him and now this is the ultimate challenge, the biggest fight of 2016."
Golovkin, 34, has secured knockouts in 32 of his previous 35 fights, including all of his world title outings.
