The former IBF welterweight champion is set to take on pound-for-pound superstar and WBO king Terence Crawford on 14 November after linking up with Bob Arum’s Top Rank.
Despite landing arguably the biggest fight of his career, the Sheffield fighter could not resist criticising Hearn for not showing what he claimed as loyalty to convince Matchroom’s partner Sky Sports to buy the fight.
Premier Sports have stepped up to buy the exclusive rights for the world title fight, despite Brook fighting on Sky for the majority of his career and conceding he was “absolutely gutted” at the failure to strike a deal.
Brook appeared to also rile Hearn with his claims that he “got him [Hearn] out of jail” when he agreed to fight Gennady Golovkin in 2016, while claiming the promoter was “more interested in signing books [than making fights]” ahead of the release of his book.
“I was really disappointed to be honest with you, and I was quite angry,” Hearn told iFL TV. "I will say this because I do feel like 99 per cent of what was said was total b*******. I do feel like I should give you the truth.
"Let's just start with the Crawford fight and Sky situation – When Amir Khan boxed Terence Crawford, Kell Brook flew out there and he was talking to Top Rank.
“He had meetings with Top Rank probably about that fight and probably about other fights as well which didn't go down very well with me to be honest with you. I'm an all or nothing kind of guy.
“I was never involved with one conversation they had with Top Rank regarding this fight, no consultation, no opinion from me, no part of the negotiations of the deal whatsoever.
“They chose to do this to all the them. Was that because they didn't wanna pay me? Or they wanted to go their separate way?
“Once you turn your back on me, don't ever turn round and start walking back to me. You're either with me or you're not.
“If you're with me, I will give you everything as I have done for that young man for eight years.
“When I talk about loyalty, I talk about sitting in the hospital with him when he spunked the weight and didn't even train for Carson Jones. Sitting in that hospital with him until five, six o'clock in the morning.
“Talking about flying out to Fuerteventura at 4 o'clock in the morning to go and deal with him and be with him in the hospital with the police there. I've been up to his house dozens of times, sat in his kitchen with him and his dad, and tried to get his career back on track.
“So don't talk to me about loyalty. And what your loyalty is – after I had to give you fights against Jo Jo Dan, Kevin Bizier, Sergey Rabchenko, Michael Zerafa, Mark DeLuca, fights that I've done my conkers on over the years – you made the decision to turn your back on me.
"I don't have a problem with that, but once you do that, you're gone, I don't have to fight for you anymore.
“Don't come back when things ain't working out and that's what they did. They chose to have me not involved in this fight and when they couldn't sell it to a UK partner, they come to me, ‘Oh I really wanted it on Sky for the fans’.
“Don't talk b*******. You wanted the most money you could get. This is the reality.”