Deontay Wilder had displayed his savage power to David Haye, who recruited the most 'dangerous' sparring partners to prepare him for heavyweight giants.
Haye was a few weeks away from facing Tyson Fury in a British battle between the former world champion and his talented younger rival in 2013.
Among the sparring partners for Haye was rising contender Richard Towers, who told Sky Sports about the punishing sessions with Wilder...
Who joined you for sparring at Haye's gym?
There was me, Deontay, Filip Hrgovic, Alexander Dimitrenko, Mariusz Wach.
I was just really glad for any opportunity. David Haye was one of the first fighters that I had shown an interest in.
As soon as Deontay walked in, from the get go, he was like,' Yes, David, I'm coming! I'm coming man!'
David was on the Versaclimber and you could see he was thinking, 'I know this guy, why is he being like that?'
He just walked over, 'Hey man, I hope you're ready. I'm here for war. I'm here to prove a point.'
What were the first sparring sessions like?
I just remember Haye's trainer Adam Booth looking at Deontay and he was half uncomfortable smiling, but he kind of knew what was happening.
He got in and he punched David Haye around the ring, to the point where I was looking and thinking, 'Come on, I don't want this to go on.'
He was whispering to David and saying, 'Right, you've got to be on the ball now, because this kid is coming to fight.
'This kid can punch.'
He got in and he punched David Haye around the ring, to the point where I was looking and thinking, 'Come on, I don't want this to go on.' David Haye, there was nothing he could do.
Deontay got out and he was like, 'Bomb Squad!'
David Haye said: 'Good spar, good spar,' and Deontay replied: 'It's not over yet.'
Did Haye land his own power punches?
If you watch the sparring videos, you can see me standing outside, waiting to get in when David and Deontay are sparring.
David Haye did catch him. He caught him with an overhand right and Deontay recovered quickly and well. His legs wobbled, of course they did, David had a horrible right hand on him.
He caught me with it once and I said to Adam: 'I'm done.'
Adam said to me: 'You chose to do this.'
I thought to myself, 'I did,' and I did another four rounds after that.
The Fury fight was abandoned when Haye was cut by Hrgovic in sparring...
I was there. I sparred first with David. Filip got in next and then David went, 'Ah.' They couldn't see anything at first, because it was a deep cut.
Filip smashed me up for two rounds, he smashed Deontay up for two rounds, and he smashed David up for two rounds, and then he smashed Mariusz Wach up for one round.
Sky Sports expert Dave Coldwell's verdict
I used to take Wilder on the pads for three weeks when he first came down for the Hayemaker camp. Obviously he had that raw power.
Out of the ring, he was really, really nice, but get in the ring and he and David would have unbelievable spars. They were literally bombing each other, both landing big, big shots.
Me and Adam would say then about just how tough this kid was, because David would crash some massive right hands on him. He would take them flush. You would see a little dip in his legs, and he would go, 'Yes, good shot.' He would walk straight through it and start smashing back. He was only young back then.
People talk about David's toughness, the shots that he would take off Wilder as well, they loved it. He used to love the guys that were dangerous. Haye, if he is sparring with you, he's looking to knock you out.