A showdown between Britain's world heavyweight kings Anthony Joshua and Tyson Fury is too close to call due to their history as sparring partners.

That is the opinion of veteran American heavyweight Kevin Johnson, who went the distance with reigning WBC champion Fury in a December 2012 points loss, before suffering a second-round knockout defeat to now unified IBF, WBA and WBO beltholder Joshua two-and-a-half years later.

Fury is seen by many as the man to beat in the division, still unbeaten in 31 contests and coming off the back of a career-best demolition of feared knockout artist Deontay Wilder in February.

Joshua's stock took a considerable hit when he was stunned by Andy Ruiz Jr – another former Johnson foe – last June but he responded in style by closing out an emphatic points verdict in an instant rematch.

The 2012 Olympic champion was due to face Kubrat Pulev at Tottenham Hotspur Stadium this month before the coronavirus pandemic laid waste to those plans, meaning talk of a long-awaited meeting between Joshua and Fury has duly ramped up.

Back in 2010, a 20-year-old Joshua sparred a 21-year-old Fury in London. In remarks far removed from more recent smack talk, both were complimentary about the other's efforts.

Johnson is a seasoned campaigner across some of the most notable gyms in the sport and served as a sparring partner – as Joshua and Fury also did – for former unified champion Wladimir Klitschko.

Speaking to Stats Perform News, he explained those lessons learned underneath headguards from a decade ago will not have left either man.

"They've got history, they know each other," he explained, before pointing towards Joshua's rollercoaster win over a veteran Klitschko at Wembley three years ago.

"It won't go the way people think it will go. It's just like when Wladimir fought Anthony Joshua.

"They had history, we all had history because we all used to go to Austria and spar together. That was the central hub for all great fighters who wanted to get in with great fighters.

"AJ and Klitschko had history, Fury and AJ got history. If they never had history then I know who I would bet my money on, but they have history and they know what to look for, what to expect and what not to expect. The strengths, the weaknesses, the speed, the power – they know that already.

"That's the thing about us fighters. We need each other for great sparring but then we've got to mess around and fight each other. It's a gift and a curse.

"If someone knows you and you know that person it's a game of chess. I know your moves, I know how you are, how fast you move your pieces on the board, I know how distracting this could be and you know the same about me. So how can you say who's better?

"It's the type of fight, just like Klitschko and AJ at Wembley. I was there and I couldn't bet a dollar because I knew they knew each other."

Nevertheless, there seems little doubt where Johnson's loyalties would lie if the blockbuster bout comes to pass.

After facing Fury, he became well acquainted with 'The Gypsy King' and his fighting family – most notably his cousin and fellow heavyweight Hughie Fury and uncle and former trainer Peter Fury.

"The Furys are my favourite team in the whole world. Not only did they open their gym up to me, they opened their home up to me," Johnson recalled. "Those are the most humbling stories.

"When I had the fight coming up with Anthony Joshua, Peter called me and said come on over and they'd help me out.

"We were running every morning, one hour uphill on a road in Bolton. We did everything together.

"I had Tyson Fury, I had Hughie Fury. I was sparring with everyone.

"If anybody ever says anything about Furys, they've got a problem with me."

Johnson will fight fellow former world-title challenger Mariusz Wach at a behind-closed-doors event in Poland next Friday, as boxing emerges from the COVID-19 shutdown.