Following the emotional admission in front of his fellow recruits, the 27-year-old took his seat where he broke down in tears.
"We did everything we could as a family — and for Jaimi— to try and bring her out of it but unfortunately that wasn't the case," he later told the camera.
"Everyone wants to do the best they can for the people that they love.
"But when you can't it makes you question yourself, 'Am I a good enough brother?'
The lifeguard also got raw over his sister's death in an interrogation with DS Ant Middleton and Jason 'Foxy' Fox.
"I remember with my sister passing ... we're all sitting there around the hospital bed with her, saying our last goodbyes, and I just remember seeing them sitting there holding her hand just being like: 'What more could we have done?'" he admitted.
"Mum said it perfectly, she was fighting a demon in her head but unfortunately the demons got her in the end... it was good in a way because it was almost as if her suffering was over."
Jett said Jaimi held on for another nine hours after he said his goodbyes, with the family deciding to turn off her life support.
"Everyone knew Jaimi as the bright, bubbly, person that she was but when you've got to live with mental health every single day it's not always sunshine and rainbows. It's the dark storm and rain that comes with it," he said.
"It's my older sister, I still love her."
Jett's mother Lisa took to Instagram after the episode aired to share how proud she was of her son.
"Jett, you have given us so many reasons to be proud of the young man you have become, for all the things you do, the kind, humble , funny, caring person you are known for - this is why people love you and this is why for dad and I, our proudest moments are when we can tell people that you're our son," she penned.
"I know it took a lot of courage to say what you did and we all know how hard it is to say the words out loud , but you know that Jaimi would be so proud of you- she always was, and she loved you so much, always her little brother. Stay strong my beautiful boy."
This story originally appeared on our sister site Now To Love
WATCH BELOW: Jett Kenny and Lily Cornish dance up a storm in Dancing With The Stars