On September 23, 2017, Campbell went 12 rounds with revered Venezuelan Jorge Linares in a world title fight in Los Angeles.
The challenger from Yorkshire was knocked to the canvas in the second round and, for a moment, looked out of his depth, but he fought valiantly for 10 more brutal rounds, doing sufficient damage to convince one of the judges at ringside to give him victory by two rounds.
Two other judges, though, saw it differently and gave Linares the win. Campbell’s first chance at a world title had ended agonisingly short.
But it was a performance of immense courage, not just for the 12 rounds of physical punishment he had to endure but also for the secret he had been forced to bury.
For just two weeks earlier, Campbell’s father Bernard died after a long battle with cancer.
The 29-year-old boxer, for whom his father had been a constant source of support and inspiration, kept the news quiet in the days leading up to the fight so as not to show weakness to the Linares camp.
He never used it as an excuse either, but talking about it in the immediate aftermath and again this week, it is clear just how much of an emotional toll it took.
“It was one of the hardest things I’ve ever had to do,” Campbell told The Yorkshire Post.
“In the days after the news and in the lead-up to fight I’d get palpitations and go into panic attacks whenever I’d think about him.
“It was a really tough period for me emotionally.
“Anytime I wanted to think about my dad or what had happened it would take a lot of emotions for me to fight it.
“Anytime those thoughts came into my mind, I had to force them out because of the panic attacks they were leading to. I was out there on my own, away from my family, dealing with all that. It was a very tough time.
“It took an awful lot of energy to suppress those feelings. I probably burnt a lot of energy leading up to that fight.”
Of the 20 bouts he has had in the professional ranks – 18 of them wins – and in an amateur career highlighted by Olympic gold in the bantamweight division at London 2012, the loss to Linares is arguably the fight he is best known for.
It is often the case with fighters; defeats in which they dig deeper into their reserves than they have ever done before tend to endear them more to the public and the pundits. Tremendous courage trumps domination in the court of public opinion.
“I honestly do think I won that fight,” reflects Campbell.
“I went into his back yard, the venue his promoters chose, everything was in his favour and everything was against me.
“But I loved that. I loved the warrior element to it. It inspired me and I maintain that I won that fight. I would love to get a rematch.”
That, for now, will have to wait for the future. For more immediate matters is atonement of another kind.
At Wembley Stadium tonight, in front of 90,000 fans on the undercard of the Anthony Joshua versus Alexander Povetkin world heavyweight title bill, Campbell fights Frenchman Yvan Mendy, the first professional to inflinct defeat on Campbell.
Three years ago, the unbeaten Campbell was riding the crest of a wave after chalking up his 12th successive win and biggest to date, defeating fellow Hull fighter Tommy Coyle in front of a packed house at the city’s KC Stadium.
Four months later, he stepped into the ring against Mendy at the O2 Arena in London and knew something was not right.
“I regretted that I got into the ring with him at all that night,” says Campbell, who lost a split decision and with it the WBC intercontinental lightweight title he had claimed by beating Coyle. “It was a tough leaning curve and I didn’t need to get into the ring with him.
“To be honest, I don’t really look back on or think much about it. It’s all part of the process. I won the Olympic Games by having defeats on my record. I had a few blows but I kept coming back and kept going.
“It was three years ago and I’ve come a helluva a long way since then.”
Campbell set about rectifying the mistake by gradually, and quietly, building his record back up. He beat Dewsbury’s Gary Sykes for the Commonwealth title, Argenis Mendez in Leeds on the undercard of a Josh Warrington bill, Derry Matthews in Liverpool and Darleys Perez in the early evening of another Joshua bill at Wembley Stadium.
Defeat to Mendy may have knocked Campbell off the top of the bill but it did not knock his desire. When the Linares opportunity came up, even though it was in Los Angeles and he was a massive underdog, he jumped at the chance.
A second defeat did not knock his career trajectory either. A knockout victory over Troy James in May got him back on the winning track, and as he prepares to face Mendy once again – the Frenchman now WBC Silver lightweight champion – there is no question he is ready second time around.
“How different am I to the fighter of three years ago? I would wupp the ass of the me of three years ago,” says Campbell, who has been working with Shane McGuigan in the lead-up to this fight.
“I’m bigger, I’m stronger, I’m wiser. All round, I’m a better fighter. You’ll see that tonight. I expect a tough fight. Mendy is a tough fighter, he’s strong, he’ll come forward and he’ll be the best Yvan Mendy he can be.
“But I’m focused on what I’m going to do. I’m not bothered about what went before, I’m only interested in what I can do now.
“It’s a massive opportunity for me, I’m probably fighting on one of the biggest shows there’s ever been. This is what you box for, nights like this.”
Win tonight’s WBC final eliminator and another world title shot beckons, but Campbell has belatedly come to realise that you take it one step at a time.
“I’ve never had things come easy, things have always taken that little bit longer to sink in, but once I get to where I need to be I’m fine,” he admits.
“I’m proud that I got to be the best I could possibly be in the amateur ranks, and now I want to be the best I can be in the professional ranks.
“There have been sacrifices along the way, I’ve been making them since the very first day I walked into St Paul’s ABC in Hull.
“Back then I chose not to party or go out drinking. I didn’t do anything that would get in the way of my boxing.
“In later life that sacrifice is being away from home, training without that family network around you. But I wouldn’t have changed any of it.”
Wife, children and family will be there supporting him tonight, when, hopefully, thoughts will be of the present and an exciting future in the sport.
But memories of last September will not be far from the surface.
“Dad always believed I would win an Olympic gold medal and I never believed him,” says Campbell.
“Then he would say he believed I would become a world champion... and I will be.”