The pair started off their careers in Take That together until Robbie left to go solo in 1995 - a year before the rest of the group disbanded.
Gary's own solo career eventually stalled, while Robbie enjoyed years of success and began publically attacking his former friend.
Gary explained: "All those years I'd just imagined this moment to actually be sat there opposite this person who had done so much damage and said so much bad stuff. Not to my face, in records and in print. It was the way it was being done that hurt."
Following the failure of his second solo album, 1999's 'Twelve Months, Eleven Days', Gary turned to food for comfort, eventually reaching 235 pounds, which he describes as a manifestation of depression.
He added: "I was shoving it in my mouth, but it was more of a reaction to who I'd been. I'd decided, 'OK, nobody wants me, but I don't want to do it anyway, and to make sure I don't do it again, this is how I'm going to look."
He eventually put his differences with Robbie aside, paving the way for him to rejoin the group for their 'Progress' album in 2010 and this year's 'Progress Live' tour, something which Gary admits was a cathartic experience.
He told Radio Times magazine: "To eventually be sat there opposite [Robbie] was liberating. And you know what, a lot of people don't get that chance, they spend their whole lives as enemies and don't talk. So for me it was a victorious day. And we came back to it a couple of days later and did some more and we were washed and we were clean."