As the Gold Logie winner talked about his battle with drug addiction and his sister Connie's cancer diagnoses, Do was left speechless and – at times – on the verge of tears. 

Johnson said he'd never forget the moment he found out his sister was first diagnosed with cancer. At the time the bone tumour was discovered, Connie was just 11-years-old. 

"Dad was just white," he said. "I remember it so clearly. I followed him inside, and he was curled up on the couch in the foetal position, sobbing. I really don't remember life before my sister had cancer."

Despite the grim prognosis, Johnson said his sister overcame the first bout of cancer. However, when she turned 22 doctors found cancer in her womb.

Connie powered through, "miraculously" having two kids after the second round of chemotherapy. 

"She's always been our little miracle girl," Johnson said. 

But tragedy struck once more in 2006 when the actor's girlfriend took her own life. 

"I'm still very upset for her and for her family," he said. "I definitely say it's probably my life's biggest sadness. And in a way, the more time goes by, the more it hurts. You know how they reckon that you come to terms with your grief as you go along? Not with this one." 

Even after having to process his girlfriend's death, Johnson refuses to call himself a "victim". Instead, he chooses to focus on life's positives. 

"I don't know whether I'm just bullshitting myself or not, but I see my time with Lainie as a gift," he said. "I lost her earlier than I would have liked, but ... I got to share my life with her. You don't always get as much of your loved ones as you want. But you get them, don't you?"

The conversation then turned to how Connie, now with two young children, is having to farewell her loved ones because the cancer has returned. This time, it's terminal – with the mum of two making the difficult decision to withdraw from treatment. 

"F--k cancer," Johnson said. "I'm so f-----g sick of it, seriously. I don't appreciate the way it indiscriminately attacks our families." 

The Johnsons have been using their final weeks together to raise millions of dollars for cancer research. Reflecting on the pair's remarkable fundraising efforts, Johnson said his sister has been a "great educator". 

"The organisation's called Love Your Sister, but underneath all that it was Connie wanting to make me right before she goes," he said. "She didn't just want to remind every mum in the land to be breast-aware. She wanted to fix me up during the process. She rescued me, by teaching me that there's more to life than me."