Anthony Joshua prepares for his conquest of America

Anthony Joshua trains ahead of his fight with Andy Ruiz Jr. in New York on June 1. Alex Livesey/Getty Images

The ramparts surrounding the private world of heavyweight champion Anthony Joshua parted briefly in Sheffield for him to discuss Andy Ruiz Jr, drug cheats, expectations and those annoying rivals before his departure for New York.

Joshua fights Ruiz at Madison Square Garden on June 1 in defence of his heavyweight titles; Ruiz officially replaced disgraced Jarrell Miller on Tuesday, two weeks exactly after Miller's first failed drug test was revealed. "I'm not going to kick a man when he's down," said Joshua. "Miller has some issues and he has to now sort his life out."

Joshua leaves for America on Sunday and his first fight there since he was a novice amateur, a skinny kid boxing for the Finchley club on a charity night in Las Vegas in 2010. "I'm going back as a man, as the champion and that gives this fight something special - I have to look good, this is more than just a fight," continued Joshua.

Ruiz was selected from a dwindling list of credible men, a list compiled by Joshua and his promoter, Eddie Hearn. Ruiz was just a few days away from his last fight when the first of Miller's three failed tests was revealed; he won the fight, joined the list and met the requirements. "He will come to fight - I know that - and he's a fast starter. I have to answer any of the problems he brings. That is what I do," said Joshua.

Ruiz has lost just once in 33 fights, a tight and disputed decision for the vacant WBO heavyweight title to Joseph Parker in New Zealand in 2016. Miller's departure and the absence of his wit, foul-mouth and belief will be missed, but the New York fight belongs to Joshua and his planned American conquest. Joshua knows what he has to do and what people want. He said: "They don't want to see a 12-round points win - they want to see a knockout, a stoppage. I know what is expected, this is the entertainment business." Ruiz will play his part in Joshua's Garden party.

In Sheffield, at the now familiar pre-fight open day, Joshua was as relaxed as ever, discussing his new boots (they have more support) and the fights that his two rivals, Deontay Wilder and Tyson Fury, have planned over the next month.

"It's a great time for the heavyweights and I hope they keep winning," insisted Joshua. "We made offers to both of them - it didn't work out at the time. I hope it does in the future. But, they should have taken me then, now I'm a better fighter, a smarter fighter."

Joshua will stop briefly in New York before setting up the final part of his training camp in Miami. In Miami he will use a secret unit to finish his camp, preparing behind bolted doors just as he does in Sheffield, where he is always a long, long way from public scrutiny. He will be taking his sparring partners with him, including the extras added when Miller was caught and Ruiz was slowly placed at the top of the list. It is not quite like-for-like, but Ruiz and Miller are not vastly different from each other. In October 2017, at just 11 days notice, Carlos Takam replaced Kubrat Pulev; the pair were very, very different. Joshua adapted, had to forget ten-weeks of training camp and stopped the resilient Frenchman in ten bloody rounds. The transition here is much smoother, but the winning stakes are also much higher.

"He is driven," claimed Robert McCracken, the coach who has worked with Joshua since before the European amateur championships in 2011. "The challenge here is not just Ruiz - it's also America. The fight is about more than Ruiz or Miller. And he never overlooks or underestimates an opponent: Joshua never drops off, I have no fear of that."

In the Sheffield ring on the pads with McCracken there were a lot of simple, jolting jabs, the ideal punch to soften Ruiz in the anticipated and fast early rounds. There was also tremendous emphasis placed on a high, high right hand guard. Ruiz never looks like a peak athlete, but he is deceptively fast, powerful and nimble. The right hand will help Joshua block Ruiz's looping left hooks, which is a troubling punch and one Ruiz likes to throw against taller opponents; most of Ruiz's opponents are four or five inches taller than him and he knows how to connect. He is good at making physical discrepancies vanish against the modern giants of heavyweight boxing.

"It's my job to be smarter on the night," continued Joshua. "I have to give the crowd what they want, but I must be smart at all times. I'm getting smarter and that means better with each fight."

Joshua also knows that Ruiz has strength, can grapple and hold in close and also use his hit and hold technique as a working part of his plan on any given fight night. Joshua has been using one sparring partner for the man's strength, his ability to hit and hold and push against Joshua's own strengths. The best fighters can make fights look like slugfests, but deliver secret, sweet science to control the action. Joshua is now starting to talk and act like a boxing scholar and not the lunatic fighter he was back in April of 2017 when he had that memorable brawl with Wladimir Klitschko. "That was a great fight to watch - I'm different now, I had to adapt and learn," said Joshua.

In the Sheffield gym, which is the headquarters for GB boxing, there are giant pictures of every single British boxing Olympic medalist since the glorious games in Melbourne in 1956. Some are known, some forgotten, some still developing, but all are gazing down on Joshua from the walls. He carries a fair few torches when he steps in the ring: boy from Finchley boxing club, Olympic gold medal winner, world heavyweight champion and now man on a mission. "I'm going to New York to show everybody how we do it," he said. The Joshua show is most definitely on the road.