DALLAS - Heavyweight Dillian Whyte was allowed to fight last Saturday despite a positive drug test because he had been cleared in a previously undisclosed hearing by UK Anti-Doping, Matchroom Boxing promoter Eddie Hearn told ESPN.

Whyte survived a ninth-round knockdown and won a unanimous decision -- 116-111, 115-112, 115-112 -- over Oscar Rivas to claim the WBC's vacant interim heavyweight title at the O2 Arena in London on a card Hearn promoted.

During the week of the July 20 fight, the results of a random test conducted on June 17 by UKAD, which oversees drug testing in the United Kingdom, came back positive for the banned steroid dianabol in his A sample. The results of Whyte's B sample have not yet been returned.

Hearn, who is in Dallas to promote Saturday's night's Maurice Hooker-Jose Ramirez junior welterweight title unification fight, said when UKAD found out about the positive test during fight week it acted quickly and convened a hearing to discuss the matter with Whyte and his representatives, though Hearn said he was not present.

"Dillian Whyte was not suspended by anybody and the British Boxing Board of Control approved him to box," Hearn said. "Prior to the fight taking place there was a hearing during the week of the fight where Dillian Whyte had to provide information. He was cleared and approved to take part in the contest... It wasn't like he failed the test and they said, 'Don't worry about it.' They had a hearing."

Whyte expressed frustration about the situation on social media.

"I am so disappointed with the rubbish that has been said about me over the last few days," he wrote. "I have lawyers dealing with it and I have been told that I can't talk about it for good legal reasons. I was cleared to fight and I won that fight fair and square."

Whyte (26-1, 18 KOs), 31, of England, and Rivas (26-1, 18 KOs), 32, a Colombia native fighting out of Montreal, also were enrolled in Voluntary Anti-Doping Association drug testing for the bout, something Whyte has done for several fights. None of those tests were positive, including samples taken June 15, which is why the WBC, which works closely with VADA on its mandatory Clean Boxing Program, was not informed of the positive UKAD test.

"At of the time of the publication of this release, the WBC has not received any notification from anyone about a positive anti-doping test allegedly yielded by Dillian Whyte in connection with last Saturday's fight against Oscar Rivas for the WBC interim heavyweight championship," the WBC said in a statement on Thursday. "The WBC has requested that the (British Boxing Board of Control), as the local governing entity that oversaw that fight, formally provide any available information to the WBC.

"The fight's promoters contracted the Voluntary Anti-Doping Association to perform prefight and after-the-fight anti-doping tests on both fighters. The WBC is not aware that any of the test results VADA has received up to now have yielded any adverse findings. The WBC created the Clean Boxing Program, which is administered by VADA, and which is a top priority of our organization. The WBC will not make any comments about the situation at hand until it receives the proper, formal communication from the BBB of C."

Rivas and his team were also in the dark about the positive test, which was first reported by BoxingScene on Wednesday.

"It is with great stupefaction we have learned (Wednesday) on BoxingScene the news about the testing result of Dillian Whyte before the WBC (interim) title (fight) against our Oscar Rivas," Yvon Michel, Rivas' promoter, wrote on social media. "Up to this moment nobody on the concerned parties have confirmed or denied to us this information."

As for why Rivas and his team were not informed of Whyte's test result, Hearn said, "UKAD cleared him to fight. When a fighter is cleared to fight by a testing agency how do you then go to (Rivas) and say, 'Just to let you know there was an issue with a drugs test but that's all been cleared up now.' The most important thing is there was a hearing before the fight and the accusations are it was just swept under the rug. But a proper organization heard this case and approved Dillian to fight.

"All the rules were followed. There was a query, there was a hearing, he was cleared to fight and the fight's on. Once the fight's approved the fight's approved."

Had Whyte failed a VADA test, the results would have been reported not only to the Whyte camp and British regulators but also to the Rivas team.

UKAD declined to comment on the situation.

In 2012, Whyte tested positive for stimulant methylhexaneamine following his ninth professional fight and was suspended for two years even though UKAD accepted his explanation that the banned substance entered his system as a result of his taking an over-the-counter nutritional supplement.