It all started with an off-hand comment: "I miss my mum," he told Jess.
Inquisitive, Jess asked what she was like.
"Caring, loving, the most generous mum ever. She's always worked three or four jobs just to keep a roof over our head," he described.
That seemed to be the trigger, Jack then began crying as Jess mused later to the camera: "All of a sudden this story and the history of his relationship with his family came out."
Describing what happened when he first rose to fame in 2011 after winning Australia's Got Talent, Jack explained: "Our relationship has been hard over the years.
Like when I won [AGT] our dynamic completely switched and I was the bread winner. The power dynamic with my mum being a single mum really changed.
"There was nothing she could do but I felt like I was almost parenting myself. I have so much resentment now that I can't control," he said through tears.
He went on to say the I'm A Celebrity jungle had caused those feelings to resurface.
"I think in here I'm just reflecting on how I wish I'd treated her better," he admitted.
Ever the supportive, Jess comforted Jack, saying: "People that aren't kind don't wish that they'd treated people better.
"There would not be a mum on this planet that wouldn't be proud of you mate," she later told the camera.
"You'd have the best teeth in the family!" she quipped, making Jack laugh.
The emotional scene was undoubtedly one to remember, and provides another perspective on Jack's life behind the scenes.
And perhaps more so than anything else, it served as a reminder that not everything is rosey, despite what things might look like on the outside.
Jack's vulnerability on the show is exactly what Australian audiences are responding to, and no doubt he'll get plenty of admiration and support for his brave confession.
This article first appeared on our sister site Now To Love.