Back in 2003, the former Westlife singer had made an appearance on Saturday morning TV show 'SMTV Live' - hosted by Ant Mcpartlin, Dec Donnelly and Cat Deeley - when he received a phone call from Simon, who had helped guide the band to pop stardom, who bluntly told him ''you look a bit fat kiddo''.
But rather than be offended, Shane appreciated Simon's honesty.
Speaking on 'Loose Women' on Tuesday (29.08.17), the 38-year-old star shared: ''Basically, it's a day I will never forget. Westlife spent every year and album with Simon. It was around the third album, Westlife was massive at the time. When everything is going great, you maybe lose the run of yourself a little. I thought I was looking alright. I flew back to Ireland after doing 'SMTV Live' and got a call that evening. I put on weight and I didn't realise. I never really struggled with weight but this year I did. Nobody else was telling me. I got the call and I knew it was him. It's usually important if Simon calls us. He said, 'It's Simon. You look fat kiddo. I was watching the TV today and you look fat. Nobody else would you. It doesn't suit you kiddo.'''
After Simon broke the news to him, Westlife's manager Louis Walsh told him that he'd noticed he'd been piling on the pounds but hadn't wanted to say anything for fear of upsetting the 'Flying Without Wings' hitmaker.
Shane - who has just released his new solo album 'Love Always' - said: ''My world just swallowed me up. Louis Walsh agreed with him after he told. He was like 'I didn't want to tell you.' ''