Dillian Whyte tells Sky Sports about punishing days with Wladimir Klitschko as he joined Anthony Joshua and Deontay Wilder in an unforgiving training camp.
Waiting to trade punches with a formidable champion, Whyte watched as Klitschko calmly dissected his sparring partners before delivering a final, concussive blow.
Any sign of submission was an insult to Whyte, who had tested his toughness on street corners and against battle-hardened fighters in little-known leisure centres, but now he was sizing up the Ukrainian ruler of the top division.
"I was just trying to learn, and then I saw him knocking people out. I was thinking 'you ain't f**king knocking me out.' I went in there and I went after him."
Whyte had headed to Klitschko's remote training base at the Stanglwirt resort, with its cosy log cabins in the snowy Austrian mountains. Away from the fairy tale façade, Klitschko was bludgeoning a parade of fighters as he prepared for yet another defence of his unified heavyweight titles.
Sam Sexton, an aspiring contender from Norfolk, had also made the trip to test his skills against the division's dominant king, only to be left with a painful memento.
"He broke Sexton's nose," recalled Whyte. "I said 'nah. Woah, you're not knocking me out. I'm coming'.
"I went in there and started roughing him up and having a proper fight with him. I got sent home for that."
Whyte would return, having received another invite to join a crop of talented fighters, including British rival Anthony Joshua, and they would be ushered into the indoor tennis courts at Klitschko HQ, which had been transformed into the setting for a far more brutal pastime.
Recent remarks from Joshua had angered the snarling south Londoner and a member of Klitschko's training team had to prevent a furious confrontation.
"I wanted to punch Joshua up, at first, because he was talking a lot of smack," said Whyte.
"There was genuine annoyance there. Bashir [Ali] and a couple of guys stopped me getting at him and then it sort of got squashed. It was a bit edgy."
Whyte says an initial offer to spar with Joshua was accepted, but later declined, with both fighters already on a collision course for their eventual British title battle in 2015.
Joshua would later lock eyes with Klitschko at the centre of Wembley Stadium, although years ahead of that epic battle, pleasantries were exchanged between the fellow Olympic gold medallists.
"He was friendly with the likes of Joshua," admitted Whyte. "They are very similar in their mindset and their behaviour. You know me, I was just a bit of a street thug then. I was just thinking, I'm not getting knocked out."
Deontay Wilder flew in for a stint at the Stanglwirt while he was still in the fledgling stages of a career that has seen him crowned as America's long-reigning WBC champion.
This younger version of 'The Bronze Bomber' strived to showcase his power against Klitschko, with Whyte revealing how he witnessed the sudden, explosive ending of a sparring session.
"I've seen him getting knocked out," said Whyte. "Wladimir knocked him out.
"He knew what happened. He had his hands up. He was roughing Wlad up, bringing the smoke, and he was going wild.
"Wlad backs up, changes his footwork, feinting, feinting, jabs to the body, throws that feint jab, left hook. Wilder had his hands up, he was gone.
"It wasn't no knockdown, he was knocked cold. Properly twitching as well.
"That's why they probably didn't want him to fight Wlad, because Wlad was going to fight him as a pro and Wilder never fancied it the whole time."
Joshua and Wilder now hold all the world heavyweight titles between them, years after they stepped between the ropes for a painful tutorial from Klitschko.
Both champions could soon be challenged by Oleksandr Usyk, another graduate from Klitschko's sparring school of hard knocks, who stepped up a division after becoming undisputed cruiserweight champion.
But what about Whyte? Will he become the latest heavyweight student from the Stanglwirt to emerge as a world champion?
"You know what. I'm going to become a world champion, regardless anyway, whatever Klitschko thinks or believes it, I don't care.
"I have the mindset, I have the hunger, and I'm good enough. I still haven't peaked yet, I'm still getting better."