However, one boxing fan took to Twitter to slam three boxers - Dillian Whyte, Tyson Fury and Big Baby Miller - all of whom have accused the 29-year-old Brit of "cheating" in the past.
The title fight was scheduled for June 1 at Madison Square Garden.
"We have now received news from Vada [the Voluntary Anti-Doping Association] that Jarrell Miller has now failed a second separate test for a further substance", Hearn tweeted.
"Believe me, this fight is going to happen", roared a jovial Wilder from his Alabama training camp hours after the Miller bombshell dropped.
A day earlier, Miller had vehemently denied wrongdoing, insisting: "The facts will prevail and I shall be vindicated". I handled it wrongly, and I'm paying the price for it.
"I missed out on a big opportunity and I'm hurting inside. If I fight him, it's definitely going to be a test and all the truths will come out".
ESPN reported on Friday that Miller had also failed a second test for another substance.
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This is the third time that Miller has failed a drug test.When he competed as a kickboxer under the GLORY banner, he was suspended for nine months by the California State Athletic Commission after testing positive for Dimethylamylamine, which has been used in the past by athletes as a dietary supplement and a performance-enhancer.
"My heart is bleeding right now, I hurt my family, my friends, my team, my supporters, but most importantly I'm going to own up to it, deal with it, and I'm going to come back better and I'm humbled by the experience".
"I'm learning this business as I go on and I know what me and Joshua means to the sport of boxing".
The 20 March sample showed traces of a substance called GW1516, which is banned because it can improve aerobic power and endurance.
Joshua still plans to make his U.S. debut as planned in June for what will be his seventh title defense.
Hearn said a new opponent for Joshua will be announced next week.
Joe Joyce, Joseph Parker and Hunter are all said to be in the running but New Yorker Adam Kownacki, who would have been an ideal replacement on account of his local credentials, has ruled himself out of the running.