Anthony Joshua has admitted that Joseph Parker's jibes about his supposed glass jaw and being the "king of steroids" has gotten under his skin, and he is intent on making the Kiwi champion pay.

Joshua will put his WBA, IBF and IBO belts on the line against the WBO champion Parker at the Principality Stadium in Cardiff on April 1 (NZ time).

The British heavyweight star accused Parker and his camp of making up lies about him being put down in the gym and using steroids to hype the fight.

Read more: How Joseph Parker's clever ploy secured Anthony Joshua showdown

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"Three times it's happened," Joshua told The Guardian.

"If you want to use it as a PR stunt carry on using it as a PR stunt, but let's just talk about facts if you want to talk real. It gets under my skin.

"If he's better than me, quicker than me, tougher than me, it will take a lot to put me away because I won't stop coming."

Joshua defended his clean doping record saying he was not only regularly tested by the UK Anti-Doping but also paid extra to be on the Voluntary Anti-Doping Association testing programme. At one point, he said drug testers even followed him to Nando's.

"I give them a slot and they can turn up anywhere, if I'm on holiday, at a hotel, at a club," he said.

"I just text them and say I'm going to be here. You have to let them know. I normally give them the time when I'm going to be in the gym training for the opportunity.

"You have to go through the piss test before they take your blood. So I said: 'Look, I haven't eaten, I'm not going to sit here for an hour.' So they have to follow me, I got in my car. We went to eat at Nando's. They were patient. Then they followed me home."

Anthony Joshua and Joseph Parker square up during their fight Press Conference. Photo / Getty Images
Anthony Joshua and Joseph Parker square up during their fight Press Conference. Photo / Getty Images

The 28-year-old said he was in the best shape of his life and warned Parker that he has improved significantly since his middling performance against Carlos Takam in October.

"I am leaps and bounds ahead compared to the Klitschko and Takam fights," said Joshua.

"I'm watching what I eat, running further and doing more than I did last year. Last week I did 20 rounds in the gym which I wasn't even doing for Klitschko, and we're still 11 weeks to the Parker fight.

"I think speed is in power. When you're heavy and you try to club these durable fighters, it's not that simple just to go 'boom'. Just because I'm the most muscly man, it doesn't mean I can just hit someone and knock them out.

"It's the shot that you don't see coming that knocks you out. When I'm quicker – bang, bang, bang – that's when I can knock my opponents down a lot easier."

The winner of the blockbuster fight will go within touching distance of becoming the first undisputed heavyweight champion of the world since Lennox Lewis in 1999.

American Deontay Wilder defends his WBC crown against highly-rated Cuban Luis Ortiz on March 3.