And that's just about time to wrap things up. If you want to read up on the fight then dive into Ben Dirs' report from the O2 right here.
Thanks for joining us and sharing your thoughts on a fight that will no doubt be talked about long into the future.
We'll have to go a long way to match it, but until next time...
Brook vows to return
"I'll be back," those are Kell Brook's final words.
He's suffered defeat at the O2 Arena, but having jumped two weights he gave Gennady Golovkin some trouble at times - trouble the fearsome Kazakh is not used to dealing with.
Brook also suggests he may be more suited to light middleweight, and says he'll be keeping tabs on Liam Smith's bout with Saul 'Canelo' Alvarez next week.
Watch this space...
GGG to return to London?
The intensity of that fight was incredible. Four rounds fought at a frantic pace, both boxers trading barrage after barrage of blows. Hardly time to catch your breath as a fan, never mind being in the ring and on the end of a huge body shot.
If Brook, like he said, was feeling nervous heading into the bout then he certainly didn't show it. And he was still standing proud despite the stoppage in the fifth. As for Golovkin's first visit to London, will that O2 crowd be enough to entice him back to the capital?
Get Involved
#bbcboxing
Neil Leverett: Kinda refreshing Ingle waved the white flag. Not enough trainers have their fighters in mind.
Adam Wildman: Brook/Golovkin was a modern day Hagler/Hearns. Brilliant fight.
Post update
Post update
Brook GGG's toughest test?
The bookies had Gennady Golovkin odds-on to beat Kell Brook tonight, and as is so often true, they didn't get it wrong.
But would things have been different had Brook not sustained that eye injury? He said he was seeing "three or four" of GGG, after all, and "didn't know which one to hit".
Brook, stepping up two weights to challenge the middleweight champion, held his own through the first four rounds, but the fifth was punishing. Too much so for Brook's trainer Dominic Ingle.
But was that the ruthless Kazakh's toughest test of his career to date?
Post update
Ben Dirs
BBC Sport at O2 Arena, London
If you missed it, here's our man at the O2's recap of that five-round thriller...
Kell Brook’s audacious bid to dethrone middleweight king Gennady Golovkin came to nothing as he was stopped in the fifth round at London’s O2.
Sheffield’s Brook, the reigning IBF welterweight champion, jumped two divisions to challenge for Golovkin’s WBC and IBF middleweight belts.
But while the challenger showed tremendous bravery and got plenty of shots through Golovkin’s defences, he was finally ground down.
And with clubbing shots raining down on Brook in the fifth round, his trainer Dominic Ingle threw in the towel.
Post update
Post update
Post update
Golovkin to fight Saunders?
Gennady Golovkin says he wants a unification fight next, and that means adding the WBO belt to his collection - is a fight with Billy Joe Saunders on the cards?
GGG hopes so.
Post update
Get Involved #bbcboxing
Golovkin v Brook
ReutersCopyright: Reuters
Helles Mannut: Intelligent decision by the corner,he would have taken tremendous damage for nothing,he has proven he's a great fighter already.
Jordan Winter: I defend Ingle. If he didn't throw it in it now it would've been two rounds later. Destructive from GGG.
Andrew Priestley: That's a brave, ballsy call from Brook's corner. There was obviously a lot of fear and concern from their camp of GGG's raw power,
Post update
Steve Bunce
Boxing pundit on BBC Radio 5 live
This has catapulted Kell into the middle of a serious boxing category in America.
Post update
'Kell deserves respect'
Getty ImagesCopyright: Getty Images
Promoter Eddie Hearn: "He would fight all night, but you can't be fighting a guy like Golovkin when you can't even focus on the guy. No one else wants to fight Golovkin, and he's given him a hell of a fight.
"I would have liked to have seen the fight go on, but Kell deserves a lot of respect."
'I didn't know which one to hit'
Kell Brook: "I'm devastated. I expected him to be a bigger puncher, in the second round I think he broke my eye socket.
"I was starting to settle into the fight but I was seeing three or four of him out there. Believe me I hurt him. When you are in a fight you can see every movement and I saw his legs buckle a couple of times.
"I would fight him again. I hope the fans enjoyed the fight. I wish it could go on, but I didn't know which one to hit.
"We will go back to the drawing board, I think I would be suited at light middleweight. I know Canelo and Liam Smith are fighting next week.
"I'm a warrior I want to carry on, you have to kill me in here."
Post update
David Haye
Former world heavyweight champion on BBC Radio 5 live
I was so happy Kell Brook's corner took a compassionate stance. I was in the same position once and seven fights later, I was world champion.
Us boxers are the last people to know. You don't know when you're in there that you can't win.
'Brook is not middleweight'
"He is a very good fighter and I'm sorry he's not middleweight, he is his weight," said Golovkin.
"I know my style and I respect him, he is good, but not so strong. So many punches, but I don't feel. I respect Kell."
Live Reporting
Alex Bysouth
All times stated are UK
Get involved
ReutersCopyright: Reuters 
Getty ImagesCopyright: Getty Images 
Latest PostPost update
And that's just about time to wrap things up. If you want to read up on the fight then dive into Ben Dirs' report from the O2 right here.
Thanks for joining us and sharing your thoughts on a fight that will no doubt be talked about long into the future.
We'll have to go a long way to match it, but until next time...
Brook vows to return
"I'll be back," those are Kell Brook's final words.
He's suffered defeat at the O2 Arena, but having jumped two weights he gave Gennady Golovkin some trouble at times - trouble the fearsome Kazakh is not used to dealing with.
Brook also suggests he may be more suited to light middleweight, and says he'll be keeping tabs on Liam Smith's bout with Saul 'Canelo' Alvarez next week.
Watch this space...
GGG to return to London?
The intensity of that fight was incredible. Four rounds fought at a frantic pace, both boxers trading barrage after barrage of blows. Hardly time to catch your breath as a fan, never mind being in the ring and on the end of a huge body shot.
If Brook, like he said, was feeling nervous heading into the bout then he certainly didn't show it. And he was still standing proud despite the stoppage in the fifth. As for Golovkin's first visit to London, will that O2 crowd be enough to entice him back to the capital?
Get Involved
#bbcboxing
Neil Leverett: Kinda refreshing Ingle waved the white flag. Not enough trainers have their fighters in mind.
Adam Wildman: Brook/Golovkin was a modern day Hagler/Hearns. Brilliant fight.
Post update
Post update
Brook GGG's toughest test?
The bookies had Gennady Golovkin odds-on to beat Kell Brook tonight, and as is so often true, they didn't get it wrong.
But would things have been different had Brook not sustained that eye injury? He said he was seeing "three or four" of GGG, after all, and "didn't know which one to hit".
Brook, stepping up two weights to challenge the middleweight champion, held his own through the first four rounds, but the fifth was punishing. Too much so for Brook's trainer Dominic Ingle.
But was that the ruthless Kazakh's toughest test of his career to date?
Post update
Ben Dirs
BBC Sport at O2 Arena, London
If you missed it, here's our man at the O2's recap of that five-round thriller...
Kell Brook’s audacious bid to dethrone middleweight king Gennady Golovkin came to nothing as he was stopped in the fifth round at London’s O2.
Sheffield’s Brook, the reigning IBF welterweight champion, jumped two divisions to challenge for Golovkin’s WBC and IBF middleweight belts.
But while the challenger showed tremendous bravery and got plenty of shots through Golovkin’s defences, he was finally ground down.
And with clubbing shots raining down on Brook in the fifth round, his trainer Dominic Ingle threw in the towel.
Post update
Post update
Post update
Golovkin to fight Saunders?
Gennady Golovkin says he wants a unification fight next, and that means adding the WBO belt to his collection - is a fight with Billy Joe Saunders on the cards?
GGG hopes so.
Post update
Get Involved #bbcboxing
Golovkin v Brook
Helles Mannut: Intelligent decision by the corner,he would have taken tremendous damage for nothing,he has proven he's a great fighter already.
Jordan Winter: I defend Ingle. If he didn't throw it in it now it would've been two rounds later. Destructive from GGG.
Andrew Priestley: That's a brave, ballsy call from Brook's corner. There was obviously a lot of fear and concern from their camp of GGG's raw power,
Post update
Steve Bunce
Boxing pundit on BBC Radio 5 live
This has catapulted Kell into the middle of a serious boxing category in America.
Post update
'Kell deserves respect'
Promoter Eddie Hearn: "He would fight all night, but you can't be fighting a guy like Golovkin when you can't even focus on the guy. No one else wants to fight Golovkin, and he's given him a hell of a fight.
"I would have liked to have seen the fight go on, but Kell deserves a lot of respect."
'I didn't know which one to hit'
Kell Brook: "I'm devastated. I expected him to be a bigger puncher, in the second round I think he broke my eye socket.
"I was starting to settle into the fight but I was seeing three or four of him out there. Believe me I hurt him. When you are in a fight you can see every movement and I saw his legs buckle a couple of times.
"I would fight him again. I hope the fans enjoyed the fight. I wish it could go on, but I didn't know which one to hit.
"We will go back to the drawing board, I think I would be suited at light middleweight. I know Canelo and Liam Smith are fighting next week.
"I'm a warrior I want to carry on, you have to kill me in here."
Post update
David Haye
Former world heavyweight champion on BBC Radio 5 live
I was so happy Kell Brook's corner took a compassionate stance. I was in the same position once and seven fights later, I was world champion.
Us boxers are the last people to know. You don't know when you're in there that you can't win.
'Brook is not middleweight'
"He is a very good fighter and I'm sorry he's not middleweight, he is his weight," said Golovkin.
"I know my style and I respect him, he is good, but not so strong. So many punches, but I don't feel. I respect Kell."