And fans were quick to comment on his new look on The Voice Facebook page.
"He's had so much cosmetic procedures doesn't even look like him," wrote one person.
"Jack has had some work done on his face it seems, he looks nothing like that fresh face boy we knew," commented another.
Jack won the fifth season Australia’s Got Talent in 2011, walking away with a recording contract and $250,000.
"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."
