Now 22, Jack says he abandoned his music career because it was a case of, too much too soon.
"I went from being just some kid to fame and money and everything," he told fans in a promo for the new series, which kicks off on Sunday.
"Somewhere along the line I just fell out of love with music. I quit completely. I just felt alone and at rock bottom. I haven't been on a stage in over five years."
Jack announced his return to the stage via his Instagram account - and fans were lapping up his new look!
"You look SO GOOD here," wrote one, while a second concurred, "Looking good, Jack."
Another commented, "Couldn't be prouder of you my favourite face."
