That’s what Hearn confirmed on Thursday.
Whyte beat Rivas on Saturday night on a points decision, having been dropped hard earlier in the bout.
But just days after, news emerged that the Brixton heavyweight had allegedly failed a drugs test.
According to a report in BoxingScene, the results from Whyte’s alleged failed test were only returned on July 17, just three days before the fight.
The report went on to state that Matchroom Sport, Whyte’s team and the British Boxing Board of Control knew about the result, however the fight was allowed to continue.
Speaking on Wednesday, Hearn explained why this was the case, and said he didn’t want to tell Rivas’ team because he was worried about the impact it would have on him, and because both fighters had been cleared to fight.
The Matchroom Boxing chief confirmed that both UKAD [UK Anti-Doping Agency] and the British Boxing Board of Control had cleared Whyte to fight despite the alleged failed test.
“If there’s an incident where a guy fails a drugs test and he is banned from the fight, of course you tell them,” Hearn told iFL TV.
“When a guy is cleared to fight, you’re not going to go to the other fighter on the Thursday or the Friday and say ‘just so you know, there was an issue with a test, he’s been cleared to fight, but just wanted to let you know’.
“If UKAD felt that he shouldn’t be in the ring, or the independent panel felt he shouldn’t have been able to fight, he wouldn’t have been able to fight. That was the process we went through.
“Contractually, I can’t pull a fighter from a fight when both guys are cleared to fight, both are cleared by the commission, how can I physically do that?
“I understand some of the arguments from people, but we have to follow the rules of the governing bodies and the people making the decisions. All of those were followed.
“All of this stuff, if I was you I would wait for the facts and the truth before passing judgement.”
Whyte became mandatory challenger for Deontay Wilder’s WBC world heavyweight title with the win, but his status within the organisation is now unclear.