- Golovkin defends his WBC and IBF belts at the O2 Arena.
- Brook's trainer Dominic Ingle threw in the towel in the fifth round with the Briton rocked by a series of brutal body blows.
A gripping contest is over and what a fantastic effort that was from Brook. At the start of the fifth, he stood off Golovkin as if to say, 'come on then'. The Kazakh then duly waded in with thunderous body shots that has the Briton sat on the ropes, taking an unholy amount of punishment. Brook's trainer Dominic Ingle had seen enough and the towel was thrown in. Gennaday Golovkin remains the middleweight king.
Kell Brook's camp have thrown the towel in, Golovkin wins!
Round four: A big swing from Golovkin misses, inviting Brook to score with a sharp hook, but it just bounces off the champion's chin.
Round three: This is a war. Golovkin stormed out of the blocks and delivered another series of huge body shots with his left. Brook asborbed them well, but never really got out of the corner until the final 30 seconds of the round. He is bleeding now too.
Round two: Terrrific round for Brook! Golovkin has a bloodied nose after being caught with a clean uppercut. The champoion absorbed them all, but it's promising from the Briton.
Explosive first round. Brook looked in big trouble after a thunderous body shot had the challenger stumbling into the ropes. The Briton responded terrifically, however, landing a couple of sharp jabs but it is Golovkin's round.
Here we go; the bell for the first round rings.
And here comes the champion. The man who has won his last 21 fights via knockout. The man who hasn't even been floored as a professional. For many, the best pound-for-pound fighter on the planet, Gennady Golovkin
Here he comes. The reigning IBF welterweight champion Kell Brook is making his down to the ring. Make no mistake, should he do the seemingly impossible tonight and stop Golovkin, it will be the biggest triumph in British boxing history.
Here we go. The legendary Michael Buffer is just about to get us started...
The main event is almost upon us. Can Kell Brook, having stepped up two weights, stop Golovkin?
And Haskins gets the win! Boos reign down from around the 02 Arena but Haskins holds onto his IBF bantamweight title after being awarded the win on points.
The final bell rings and both Hall and Haskins think they have done enough to get the win. It's going to be close...
It is all Hall now as the ninth round comes to an end. Haskins is gassed and was momentarily rocked by a straight right from the challenger. Hall is in the ascendancy, the champion might have to just hang on in the final two rounds.
We are into the sixth round, the round Haskins said this fight would end in. Hall probably edged that one, but Haskins' movement and effective use of the jab has been too much for him in the previous rounds.
The final fight of tonight's undercard is underway with Stuart Hall challenging Lee Haskins for his IBF bantamweight title.
How exactly has Kell Brook been preparing for the the biggest fight of life? While you're waiting for the opening bell, have a read of our piece on the 30-year-old's preparations in the humble surroundings of Sheffield Hallam University.
Callum Smith meanwhile has eased past Hungary's Norbert Nemesapat. Smith, who is the mandatory challenger for Badou Jack's WBC world super middleweight world title comfortably worked over his opponent before ending things in the sixth round with a series of superb body shots.
Already tonight, Conor Benn has extended his professional record to 4-0 after a comfortable victory over Joe Ducker. Charlie Edwards meanwhile challenged John Riel Casimero for the IBF flyweight title, aiming to become the youngest ever English world champion, but came up just short, falling in the 10th round.
There aren't many fight announcements that provide the genuine, tangible surprise felt like when Brook vs Golovkin was unveiled on a quiet Friday afternoon in July.
The Sheffield-born fighter sent a shockwave trembling through the welterweight division when he defeated Shawn Porter in the American's own backyard in August 2014, becoming the first Briton to win a world title in the United States in 28 years. Suddenly, doors were opening up in front of him. Bouts with Floyd Mayweather and Manny Pacquiao were being touted, as was a long awaited showdown with long-term adversary Amir Khan.
But after the triumph of his title victory, Brook's three title defences failed to get the juices flowing. Wins over Jo Jo Dan, Frankie Gavin and Kevin Bizier were as routine as they come, and the need for a greater test was desperately needed.
That looked to be developing as talks with WBO champion Jessie Vargas mounted. Instead, the boxing bombshell of the year was dropped when it was announced Brook would step up two weight divisions to take on the most feared fighter on the planet.
Golovkin had been vying for a unification bout with Saul 'Canelo' Alvarez, having become the mandatory challenger for the Mexican's WBC belt. Instead of taking the fight, Canelo relinquished the title, temporarily crushing plans for what many would have seen as the biggest fight that can be made right now.
Many will argue Canelo simply ducked the challenge; one Brook eagerly snapped up. Make no mistake, a win for Brook on Saturday would be the biggest British victory inside the ring in boxing history. But the weight of the challenge at hand is colossal. Golovkin has built a career on ending fights early. Only three of his 35 professional fights have gone the distance. It's been eight years since we last heard the final bell in one his bouts, his last 21 ending with an early stoppage. An average knockout rate of 91% is good enough to be the best in the history of middleweight boxing. Throughout his amateur and professional career, he has never been knocked down. His record in the ring is unblemished.
It's a frankly ridiculous set of statistics and records that see many regard Golovkin as the best pound-for-pound fighter on the planet. Somehow, Brook has to find an answer to it.