The 'Angels' hitmaker - who quit the group in 1995, a year before they split, and refused to join their comeback in 2005 - is thrilled to be back working with Gary Barlow, Mark Owen, Howard Donald and Jason Orange again but admits he would have contemplated turning his back on his career if he hadn't been asked to sing with the band again.
He said in an interview with Popjustice.com: "If it wasn't for the boys, I would probably be doing nothing because I quite enjoy doing nothing now. It does feel like the end of one of the last chapters in the book and I do feel a bit spent to be honest with you.
"I'm loving what's to come, obviously, and I'm very excited being back with the boys, our album sounds amazing, I'm excited to do the tour and all that business . But I'm kind of still at a loose end figuring out what I want to do when I grow up."
The 36-year-old singer has also admitted he "couldn't be a**ed" when recording his most last studio solo LP 'Reality Killed The Video Star' because he no longer knew what sort of music his fans wanted him to produce.
He added: "It kind of was going through the motions, because, as you know, I was all hyped up about doing 'Rudebox' and going down that road and then everybody went, 'No!'
"But I didn't want to do another 'Come Undone', or another 'Angels', or another 'Road To Mandalay' - you do find yourself sort of in the boggy marsh of then thinking, 'Well I don't quite fancy doing that anymore.' And because everyone had gone, 'No', I went, 'Well, OK, I can't be a**ed either.'
"And you know, I did find myself capitulating and going, 'Well do they want THIS then.' It's like this idea of knowing your audience - and knowing that my audience didn't like 'Rudebox' left me thinking, 'Well, er, I don't know what to do now.' "