Klitschko unconcerned by Joshua spending time in his training camp two years ago

The two are also scheduled to fight for the vacant WBA title when they meet at Wembley Stadium on April 29, in front of a likely post-war British record boxing crowd of 90,000, by which time Klitschko will be 41 years old.

In 2014 the two sparred 20 rounds together at Klitschko's training base in Austria, when Joshua remained an inexperienced professional, but the Briton is a keen student of the sport and will have learnt much from observing one of the finest heavyweight champions in history.

Klitschko, however, is adamant that regardless of how much it benefited his 27-year-old rival - Joshua had the chance to watch Klitschko's techniques in addition to sparring him - he only saw a fraction of the Ukrainian's preparations.

He also insists he has continued to adapt his training since then, even though he believes Joshua is far more of a threat than many would be after only 18 professional fights.

"There is so much: the content of the preparation," Klitschko, 40, told Press Association Sport.

"Any person or sparring partner that got into my training camp, getting a feeling for it, learning: it's fine, I want people to learn from it and I'm happy to share.

"It's definitely good for him, because he saw how a top athlete and champion is preparing.

"He definitely adjusted it to his preparations. I think he did learn a lot. I'm also trying not to stand still, and I've been observing how he's training, and how he's getting ready, and he definitely has a professional team that works for him, to make him as strong as possible."

There are obvious comparisons between when Joshua, the early favourite for the fight, will defend his title against Klitschko and when David Haye faced the Ukrainian in 2011.

Like Haye, albeit to a lesser degree, Joshua is the smaller fighter and, like Haye, he is also considered such a threat to the former champion because of the youth, speed and power demonstrated in two defences of his title. He was also vastly more experienced than Joshua, but struggled against Klitschko when convincingly losing on points.

Klitschko will be trained by the respected Johnathon Banks, who succeeded the late Emmanuel Steward - widely considered one of the greatest trainers in history - and asked if either would have allowed Joshua to meet such a dangerous opponent after only 18 fights, he responded: "Absolutely, yeah.

"Even 18 fights, it's maybe not much - but if we talk about Mike Tyson, he was 20, he was a baby to become champion - it's so relative.

"Anthony: he is more than just 18 fights. He has more than just two title defences. I truly believe in his talent, he's an amazing athlete and a good representative for the sport.

"If he's going to win then I'll congratulate him, and when I win I'll help him to come back. I've done it a couple of times already."

Klitschko was also asked why he'd agreed to fight Joshua, when he'd previously spoken of his willingness to wait as long as necessary to pursue a rematch with Tyson Fury.

He said: "I feel sorry for him so it's not a topic anymore to even talk about it, I was just focused on one thing: getting my revenge. No one was interesting to me.

"Since that doesn't exist anymore (Fury's struggles with mental health means he remains inactive), I'm looking around, and it's 'Here we go, there's Anthony, a champion', and he's absolutely a knockout machine. It's perfect, the timing is perfect."