"He looks well," Hearn said. "He looks a lot heavier. He looks more built for a tear-up than for speed last time. I think last time he might have taken too much weight off because everything was about speed. Although he was just messing about with Kevin, you could see him working on the inside and I hope that's a sign of things to come because if we get that kind of fight it's going to be an absolute barn-burner.
"The winner of this fight goes on to a great position. But the winner of this fight, if it's a brilliant fight with great performances, takes it to a whole other level and Parker can't afford another lacklustre performance.
"He has to express himself and enjoy himself and fight free and if he can do that it will be a hell of a fight.
"If he wins against Whyte he has the chance for a Joshua re-match. It's just a case of when."
Hearn clearly enjoyed catching up with his old sparring partner David Higgins, Parker's promoter, the pair's relationship formed during negotiations for the Joshua fight allowing them to seal this one in 48 hours – a remarkable achievement in professional boxing.
"We've always had a good relationship. Not a lot of people trust others in boxing. After the first fight, which was a huge success and nearly broke the pay per view records here, they [Joshua and Parker] both made a fortune. There was a great feeling about it afterwards. Joe lost his title but he is secure for life.
"Higgins, although he's a bit quirky at times, is smart, he's a lateral thinker and he's a character. The public here like him."
Parker said afterwards: "The reception's great here – it doesn't even feel like we're away from home. There's a lot of love – I can see a lot of New Zealanders here."
Whyte, who has also lost to fellow Englishman Joshua, probably needs a knockout in order to beat Parker. The 30-year-old is an aggressive and emotional character – and although he is ranked No2 by the WBC, a loss in an all-action performance probably won't hurt his career too much.
"Everyone knows I'm coming for a scrap," Whyte said. "It is what it is."
"If it's an entertaining fight it's not the end of the world," Hearn said of 26-year-old Parker. "If Joe loses in a good fight the public will want to see him back.
"I don't believe they [Team Parker] were as confident as they made out before Joshua. I do believe they are confident about this one."
Parker v Whyte on Sunday morning NZT will screen live on Sky Sports pay per view: https://fanpass.co.nz/ppv/whyte-v-parker
https://www.sky.co.nz/parker-fight-competition
Patrick McKendry travelled to London with assistance from Duco Events