The 32-year-old former English champion had been stuck at the bottom of the barrel after calling it quits the first time around.
Overweight after adopting an unhealthy lifestyle, and finding times hard in a mental capacity, his days as an elite athlete seemed well behind him.
But the ex-Sandygate ABC champion, a titleist across three weight divisions, took one last look in the mirror and told himself that enough was enough.
Now, four stone lighter from his lowest ebb during the pandemic, Singleton is ready to do it all again after a four-and-a-half-year lay-off.
"I've fluctuated in weight, my head has been all over the place, it's been crazy," he said. "I enjoyed the first 12 months after my career ended, but then I just got stuck in a routine of doing it. That's not the life for me and that's the reason I'm making a comeback at 32.
"I love the sport. I hated the days when I was out of shape and not right mentally. Those hard days training now are actually good days and I thrive on it. Everything I've been through has made me want it more."
The ex-WBC International Silver supremo at welterweight, who would later challenge Bradley Skeete for the British title, returns to the ring at the AJ Bell Stadium, the home of Salford Red Devils, tonight [Friday].
It comes nearly 13 years after he'd marked his pro bow with a stoppage against Jason Thompson at Colne Municipal Hall. "I don't think I've ever felt like this," Singleton said.
"It's weird; I'm experiencing so many mixed emotions. I've never suffered with nerves in my life, but I think I'm nervous. Boxing has been my life from eight to 28 and I don't know anything else.
"I didn't get nervous, but I've had five years out now. I'm nervous, excited and I'm really proud of myself from where I've come from. I'm going to come out all guns blazing."
Singleton, a stablemate of Seamus Devlin's at Darren Stubbs’ base in Oldham, under the guidance of former journeyman Curtis Gargano, goes up against CJ Wood, a 34-year-old adopted Yorkshireman.
The Bedfordshire-born boxer lost just one of his first six contests, beating Edgars Milevics, Vaclav Skromach and Matar Sambou, though they were on a BIBA event.
His first recognised outing under the British Boxing Board of Control's jurisdiction ended in a stalemate against Corey McCulloch at New Douglas Park in Hamilton and he has recently lost four on the bounce, including a City Hall showing at the hands of Evaldas Korsakas, a one-time opponent of Singleton.
"They were talking about 'journeymen' and I said 'forget it'," said Singleton, who'll now be operating at middleweight. "I've got nothing against them, I train with them, but I'm past that, I don't need to fight them. If I want to do 10 rounds with a journeyman I can do it in the gym. I've done it throughout my career so I just want a test.
"I picked this opponent myself; I've watched a couple of his fights. He had a decent fight with Evaldas Korsakas, who I drew with. It was a good, competitive fight, and showed that he [CJ Wood] will come and have a go. He'll try his best to cause an upset."
Singleton, who has also re-joined forces with ex coach Karl Ince, continued: "I'm fighting a better calibre of opponent, rather than a journeyman, so it's coming out of my pocket. It cost me money. I could have chosen to knock someone around for a few rounds and made myself an extra few thousand pounds. I'm not in this for the money, though.
"He's experienced, he's had 60 amateur fights and 80 unlicensed fights. He's tough and he'll scrap. I've been sparring with quite a few people, including unbeaten prospects like Leon Willings, Wycombe King and Tom Rafferty. I've been sparring some good amateur lads at Karl Ince's gym as well. I've been busy."
Shayne would like to thank his sponsors for their support: A. Kutz Barbers Shop, P&S Engineering Services, Uprite Scaffolding, Nolan K9, Janitorial UK, Intershape Transformation Facility, Canning’s Construction and Chief’s Health Kitchen.