LONDON, ENGLAND -- Alexander Povetkin insists he is not a drugs cheat despite failing two dope tests in 2016.
The Russian challenges WBA-IBF-WBO world heavyweight champion Anthony Joshua at Wembley Stadium, London, on September 22.
But two years ago his career was left in serious doubt after he twice tested positive for performance-enhancing drugs within eight months.
It cost Povetkin a shot at WBC world heavyweight champion Deontay Wilder in May 2016 and then a title eliminator against Bermane Stiverne in December 2016.
Povetkin (34-1, 24 KOs), 38, tested positive for the banned substances meldonium in May 2016 ahead of a scheduled fight with Wilder. Povetkin admitted he used meldonium, but said he used it in 2015, not after Jan. 1, 2016 when it was banned by the World Anti-Doping Agency.
Povetkin then tested positive for ostarine, a muscle-builder that has been on the WADA banned list since 2008, in December 2016.
"First of all, I have been cleared of that suspension, I have been justified, and the court case that was ongoing with the team of Wilder has finished in our favour," Povetkin told reporters.
"First I was caught on meldonium, and it was a nanogram quantity. And it happened right before the fight. I was clean a couple of tests before it, and I was cleaned when tested after that.
"For me it was very, very suspicious. I know that I am clean. I know that I was clean back then. I don't know what happened but at the end of the day, all I can say is that I was accused of wrongdoing when I wasn't.
"The second time, ostarine, I don't know what it is. When I read about it and they said it is for gaining muscle. I only weighed 100kg for that fight. A couple of tests before I was caught were clean. The tests after were clean. And the time they found it before the fight, was very, very minor in quantity.
"Doesn't it all sound a little suspicious? In my opinion there was something going on at that time? I have nothing to do with it.
"The amount they found doesn't give any affect so why would I ever want to do that. Whoever did that it's none of my business. I am clean and I know that I was clean then."
Despite his trouble with banned substances, Povetkin continued his career without a ban stopping him from boxing and on March 31 viciously knocked out England's David Price. He enters the Joshua fight as the WBA mandatory challenger after eight successive wins -- six by KO -- since his only defeat, unanimously on points to Wladimir Klitschko in October 2013 and on the same night Joshua turned professional.
"I am very well deserved of the fight I am getting, I am here for a reason, this was a mandatory," Povetkin said.
Povetkin, who won a gold medal at the 2004 Olympics, argues that Russian sportsmen and women are being unfairly judged.
Russia's track and field team was banned from the 2016 Olympics and their whole team was not allowed to take part at the 2018 Winter Olympics in response to the doping allegations.
"I don't think that our sportsman in Russia consume all those things [drugs] they are accused of," Povetkin told reporters through a translator.
"It's a bit annoying to be honest. As an amateur I understood myself what we consuming and what we were taking, and I can assure you there was nothing prohibited.
"Never was there anything out of the ordinary either for myself or the team that was offered to us, or discussed."
Joshua (21-0, 20 KOs), 28, who lives in north London not far from Wembley, says his whole career would be tarnished if he were to ever test positive.
"I would rather take a loss than be done for doping, being done for doping is far worse for your legacy than taking a loss," Joshua told reporters.
"I don't see doping as a way of making yourself better, if a person is better than you then work harder, train harder, you don't need to dope.
"Weigh it up: doping, being banned, legacy damaged or someone is better than you on the night, give them the respect and bounce back.
"I would rather stay clean and give it my best every time. When he is fighting it me it will be straight and clean fight. His past is his and past and they dealt with it however they did, if i got done for doping -- it would never happen -- then they would deal with me.
"I am on UK Anti-Doping and VADA [Voluntary Anti-Doping Association], £30,000 every time for each fight. They know your whereabouts every day."