Irwin's battle with the illness hasn't been without its obstacles, including of late a hospital stay with jaundice as well as a nasty chest infection bout.
He's also undergone chemotherapy and a number of hospice trips since his 2020 diagnosis after the illness spread to his brain and liver.
But he remains in high spirits as he continues to defy the odds set by doctors, culminating in his family's recent getaway to Spain to celebrate his 50th.
Accompanied by sons Rex, four, and three-year-old twins Rafa and Cormac as well as his wife, Irwin has reflected in a new interview about the "valuable" time he spends with his family and why he won't let it be marred by them knowing about his illness.
Jonnie Irwin alongside his wife Jess and their three children
Irwin told Hello! that his children know "absolutely nothing" about his illness before he delved into why they want to keep it that way.
The Escape to the Country star explained: "They've got bad news coming so I want them to have as blissful a childhood as possible."
Irwin's wife, 41, weighed in: "When I was told Jonnie might not live to see the twins' third birthday I was a mess. I didn't know what to do and nobody can help you with what is going to happen and how you are going to feel.
"It was important to get away for Jonnie's birthday because we honestly didn't expect him to be here, so it's really special.
"It's lovely to see him with the boys around the pool and outside in the warm weather.
"It's not just celebrating his birthday; it's celebrating that we're on holiday, we managed to get on a plane, and he's still here, which we weren't necessarily expecting."
Irwin and his other half haven't only been celebrating his 50th birthday this year, either.