The Candy singer was 15 when she was booked to tour with 'N SYNC in 1999, but the thrill of sharing a stage with her pop idols quickly wore off after an awkward backstage encounter with Justin.

"I was just the opening act. Nobody cared about me, but Justin Timberlake was there and (somehow) there was a conversation about feet or foot size," she told America's The Late Late Show host James Corden, "and all the background dancers and the 'N SYNC background dancers and my background dancers (are backstage), and I stroll up at 15, like, freaking out that Justin Timberlake is there.

"He was like, 'You have big feet for a girl'... I'm sure he doesn't remember this at all, but I was so impressionable and I thought, like, the world of him. Sixteen years later it stuck with me. It really scarred me emotionally... I was, like, going through puberty at the time... It was embarrassing."

Despite Justin's remark about her size 10 feet, Mandy, who also hit the road with the Backstreet Boys, insisted the tour with 'N SYNC was still a career highlight.

"I went from watching them ('N SYNC) on MTV as I was getting ready for school in the morning to six months later I was on the road with them," she recalled. "I went from shooting my very first music video in Los Angeles and I flew to Virginia Beach... and I started the tour."

But she hated learning dance routines: "I have no rhythm, I'm super awkward," she laughed.