For decades, the music made by the original lineup of the heavy metal band Dio had been an important touchstone for millions of people. But that legion of proud listeners was famously missing one important member: then-Dio guitarist Vivian Campbell.

Campbell, who was fired from the band after a contentious business disagreement with frontman Ronnie James Dio and band management, went on to join Whitesnake and later Def Leppard, with whom he's been a member for nearly 25 years, never looking back. The only time he spoke about Dio, it seemed, was when he was sparring with the singer in the press.

"I didn't see it as my heritage because of the really bad taste in my mouth after I was fired from Dio, and in the years after it was portrayed in the press that I was the one that had turned my back on the band, which was absolutely untrue," the Irish-born guitarist shares with Headlines & Global News in an exclusive interview. "I was fired in the middle of the tour. I never wanted to leave Dio, but it gave me such a bad taste in mouth that I didn't even own the records, I didn't listen to the music, I didn't acknowledge it, I wanted nothing to do with that part of my life or even that genre of music as a result."

So it comes as a surprise to many that Campbell recently reconvened with original Dio members bassist Jimmy Bain and drummer Vinny Appice, adding vocalist Andrew Freeman, to form Last In Line, to revisit the spirit of the music Campbell had made together with the late Dio, Appice and Bain, who recently passed away as well, on the classic albums "Holy Diver," "The Last In Line" and "Scared Heart." Last In Line, which started as a project to play the old Dio material, began composing its own songs and released its debut album, "Heavy Crown," on Feb. 19.

We spoke extensively with Campbell about why he's changed his mind about Dio music, how Last In Line came together, the challenge of promoting the album while mourning Bain, who passed away on Def Leppard's Hysteria On The High Seas cruise on Jan. 23, and his ongoing battle with cancer.

You're dealing with Jimmy's passing while releasing "Heavy Crown." How has this process been for you from an emotional standpoint?

It's very surreal, maybe even more so by the fact that the album was actually ready to be released a year ago, literally last spring, and we all talked about it and we collectively decided to sit on it for a year because we all believed in it so much that we wanted to wait until our schedules afforded us the opportunity to tour the record and to promote it. So it's particularly bittersweet that it comes out at this time, because Jimmy literally died a month before the release. He got to the 11th hour and he never got to see the release of the record. And we all truly believe in it and took such great joy in writing and recording this record and reconnecting with each other on a personal level after so many years, and probably none of us more so than Jimmy. Jimmy was battling his addictions all his life, but in the last few years it had really come to a head. The whole time we were writing and recording this record, Jimmy was actually in court-appointed rehab and he'd finally overcome the demons. For the last year and a half or two years he was stone cold sober, and part of his being able to be that way I believe was the focus he put into this record and writing these songs and being committed to us to such an extent that Jimmy even went out and had a tattoo (laughs). In his mid-60s, it's the only tattoo he had on his body was Last In Line, that's how committed he was to the band.

It's a strange, strange time. We're really at a crossroads. The record has been remarkably well-received, but we really don't know what our future holds. We were supposed to be on tour right now, and we canceled the tour out of deference to Jimmy's memory, we just didn't feel it would be respectable to get some guy to play bass and go off on tour a month after he died. So the only thing we have on the horizon we have on the horizon is a couple of festival shows, one in late April and one in May that were booked before Jimmy's passing that we will honor those commitments. I don't know what our long-term future is going to be, you know?

How did Last In Line get started?

It was my fault. Def Leppard was inactive and I got a call from Scott Gorham from Thin Lizzy asking if I could possibly go on the road with Lizzy for a few months as a stunt guitarist. I completely leapt at the chance because Thin Lizzy were the most influential band for me in my mid-teens when I was really learning my craft as a guitarist. Just being on stage playing those songs of my youth with Brian Downey and Scott Gorham, it just transported me back to being 16 again and being so focused on guitar. I came off the tour and I just wanted to play that kind of guitar again and I wanted to play rock and play guitar solos and really re-connect with my instrument.

So I called Vinny and Jimmy, and we had kept in touch, we were always close even though we didn't see each other often, we'd bump into each other in L.A. at different functions. And I said to them, "Do you want to get in a room and just be in a rehearsal room?" And fortunately they were both amenable to that, so we started playing. This was probably mid-2011, and at this stage it had been about 27 years since we had played together, but as soon as we started playing it could have been 27 seconds because the chemistry was just immediate and we all got super excited and got goosebumps, and we all looked at each other and were giddy like schoolboys. That's what started it. And from there Vinny actually was the first one to say this would be so much better if we had a singer to complete it, and I knew this guy singer, Andrew Freeman, and at the time Andrew was still living in L.A., and we called him and he came down, and when Andrew started singing, that's when I had the light bulb moment. That's when I thought this is really interesting; you have the unmistakable sound of the early Dio band and you have this singer who's powerful enough to sing over it, which you need to be to sing over that racket. I said this guy sounds nothing like Ronnie, he's got the pipes but his tonality is different, his phrasing is different. So this was really interesting. That's when I suggested that we just go out and do some shows, and I didn't really give any thought to a name. This had been about a year since Ronnie had passed away, and I just thought, we're the last in line now that Ronnie's gone. Let's just call it Lost In Line, and we all looked at each other and went, yeah, let's do it. We wouldn't have done it if Ronnie was still alive. Dio the band was still out there in some incarnation making records and touring. It would have been weird, but I think it was also the fact that Ronnie had passed away that made it seem OK to me to do it, and perhaps to Vinny and Jimmy too, that we were not competing with that, with that history and the whole Dio thing.

[Being fired from Dio] left me so hurt. Ronnie and I were both guilty of saying hurtful and stupid things about each other in the press, which is never a good idea. But maybe it was also because Ronnie had passed away for a year or so that I was able to come back to that part of my life and career and embrace it and recognize it and see it in a whole different way and realize that it's as much my heritage as it was Ronnie's, and it's certainly equally as much Jimmy and Vinny's. We all created on those early Dio records, we all wrote the songs. It was very, very much a collaborative effort, even though it was never really billed as such, it was a band. We created as a band in every true sense of the word.

I was going to ask if your business disagreements with Ronnie tainted your opinion of the music, but it seems like the answer is a resounding yes.

It did in a lot of ways, and it was foolish of me to make that equation, because the genre of music has nothing to do with what happened between me and Dio, but it kind of tainted it for many years. Plus I was a very young man at the time. I was in my early 20s still, and I was really broadening my horizons as a musician. I was getting into singing and singers and songwriters, and I was listening to a lot of different genres of music. When I was a teen all I listened to was guitar-driven music. It was all about guitar and guitar solos and guitar riffs and guitar playing, so I was very much drawn to that kind of music and that genre, but in my early 20s I was starting to buy Motown records, and I was really starting to listen to singers and starting to take singing lessons and really wanted to learn the craft of songwriting more, instead of just writing a guitar riff, I wanted to learn how did the singer write a melody? It became a whole different world. So that also probably exacerbated that desire to distance myself from that genre. What had happened with my being fired from Dio and the way that it happened, the backhanded way that it went down, kind of really helped push me away from the genre.

What was so special about that original lineup of the Dio band?

Well, there is a chemistry when certain musicians make a sound together, and I don't subscribe to the fact that musicians can just be replaced, that you can get rid of the drummer or bass player or singer or guitar player and it will sound exactly the same. As human beings we all have a unique fingerprint, and as musicians it's exactly the same way. We all bring in nuanced, slightly different things into the equation, and when you find three or four musicians who really work together and create a unique sound together, it's never going to be the same when you start replacing them. That's why it's particularly weird now with Jimmy's passing right on the eve of the release of the record, because I know it will never be the same. When Last In Line goes on stage next, we're going to have someone else playing bass, and it's never going to be quite the same for me and for Vinny. We're going to notice the little subtle differences that Jimmy brought to the table, and the physical way he played his bass was a big part of the sound. But you know, that's life, and if we want to continue we have to accept that and accept that difference, but we're all unique.

Now that you're revisiting these old songs, are some of the positive memories coming back?

Yeah, and there were a lot of good times, certainly when we were performing. The music was always magical. There was never an issue with that. On a personal level Ronnie and I didn't always get along. Sometimes we did, we were laughing together, but then sometimes we were not (laughs). There was conflict there. It wasn't the easiest relationship. There was a generational gap, Ronnie was considerably older than me. But there was always a force at work that was pulling him away from the band. Ronnie wanted it to be a band, and it was in the creative sense, but the longer we went on the more distance was being put between Ronnie and the rest of us by the business side, and that's ultimately what broke us up. It ended up being a matter of principle. A lot of people dumb it down to thinking it was a matter of money. It was never about the money, it was always about the principle. I've always been a very, very principled person, and when a man shakes my hand and looks me in the eye and makes an agreement with me I expect them to honor it because I honor my end of it. So that was the issue I had with Ronnie, it was a matter of principle that just happened to be about money. But it was sad. I do believe that on a musical and on a creative level Ronnie believed, as we all did, he knew that it was a great chemistry in the band and that was a magic lineup.

How is your health?

That's the least of my concerns, to be honest Mike. I'm still dealing with the cancer, it keeps coming back. It's been three years, I've done three rounds of chemo, stem cell transplant and I really thought would be it with the stem cell transplant, but no, it came back, so I'm kind of resigned to the fact that I'll probably deal with the rest of my life. But I'm really not at all concerned with it, it's just maintenance. I put it on par with going to the dentist. It's a little bit more involved than that, but it's just something that I got to keep doing. I'm one of the lucky ones. I was diagnosed early and have great health insurance and good doctors and I've always been one step ahead of it and I continue to be so and I intend to be so. It's particularly a contrast when you consider that Jimmy actually died of lung cancer and didn't even know that he had it. He was dealing with pneumonia for the last month before he died, but it turned out that the pneumonia was brought on by chronic lung cancer. Jimmy didn't even have health insurance. I feel so fortunate that I'm one of the lucky ones. In this country there are so many people who cannot afford access to proper healthcare and can't advocate for their own health, and you get these diseases that are so prevalent like all these cancers and you don't even know you have them.

You're based in L.A.?

I'm in Los Angeles, yeah, and I'm continuing my treatment at City of Hope, which is nearby L.A., and they're wonderful, wonderful doctors there. I'm currently doing immunotherapy which is the latest and greatest treatment for cancer. It's still part of a clinical trial that I'm a part of. The drugs are that new. I'm actually taking a drug called pembrolizumab, which is the same stuff that cured Jimmy Carter's melanoma recently, so it's actually the shining star of these new courses of immunotherapy drugs. So like I said, I'm very, very, very fortunate to be able to do this. I actually got great results earlier this week. I did some scans and the results show there's very little cancer activity compared to the last scan three months ago, so it seems to be doing the job, and I'm certainly feeling good, and there's absolutely minimal side effects, so it's a whole different way of treating cancer. It's good.

Does keeping busy make it easier to deal with the cancer?

Absolutely. Yeah, I've always subscribed to that thought process. When I first got diagnosed I actually had a really difficult time convincing the guys in Leppard and in particular Def Leppard's management that I could continue to do this and that it was the right thing for me to do. But my work is cathartic to me, and it's very much a big part of my treatment and my cure, and I couldn't imagine anything worse than being sidelined and not being able to go and perform live and do my work.

That's what gives me life. That's the reason that I live. You are what you do, and I'm a musician. So as long as I can keep doing it there's hope.