Joshua and Miller clashed in New York on Tuesday at a press conference for the Brit’s upcoming fight with Alexander Povetkin.
Miller has been vocal in his pursuit of a lucrative showdown against 28-year-old Joshua, signing with Hearn’s Matchroom Boxing, while attempting to position himself in the rankings for a crack at the title.
With insults directed between the pair, Hearn was forced to step in to calm matters down.
At least that’s what he hoped.
Now promoter Hearn has admitted the animosity continued following the press conference.
“It all went off the stage and I thought ‘that’s a result’,” Hearn told iFL TV.
“Then Joshua came out the toilet and Miller’s standing at the end of the corridor mouthing off at him.
“He’s running and I’m having to hold him. It was interesting.
“It’s a big day for Miller because that’s just put his profile right up there.”
Joshua will make his seventh world title defence when he takes on Povetkin at Wembley on September 22.
The Russian knocked out David Price last time out, fighting on Joshua’s undercard as he beat Joseph Parker to earn the WBO title in March.
Joshua currently holds three of the four major world titles – the IBF, WBA and WBO – with just Deontay Wilder’s WBC strap standing between him and the mantle of becoming undisputed heavyweight champion.