Since then, he's kept his loyal followers up to date on every step of his cancer journey.
"At some point it will get me, but I'm still fighting, still kicking on," Johnny told Carrie, whose husband Greg Lange died of cancer in 2010.
"Looking up my diagnosis and my tumour, the average life expectancy was three years. And for me it's now been five years.
"I'm already winning. My goal now is to try and help as many people as I can and also live a happy life."
Johnny, whose new memoir No Finish Line came out today, said he is worried about how his long-term girlfriend Tahnee Sims will cope without him.
"You can only imagine how difficult it's been for her. What plays in my head a lot is, I hate to say this, how hard it may be for her if something does happen to me," the actor said.
"So, it's something that I don't want to think about. It just gets me a little bit emotional about it because I know at some point something will happen, whether it's, you know, a month from now or 10 years from now or 20 years."
Earlier this year, Johnny praised Tahnee for sticking by his side during the toughest years of his life.
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"Without her I may not be here," Johnny told Now To Love.
"She was the one who made me get in the car [to go to hospital] when it [the headaches] first happened. And she's encouraging me to do things. She keeps me active, getting me to go for runs and swims."
This article first appeared on our sister site, Now To Love.