John Farnham reveals his harrowing oral cancer battle has left him unable to sing or fully open his mouth: 'It's a very disconcerting thing'

John Farnham has opened up about his terrifying cancer battle, which has left him unable to fully open his mouth .

The Australian singer, 75, was declared cancer-free one year ago and has shared details about the harrowing ordeal in his upcoming memoir, titled The Voice Inside.

He revealed he has been left unable to sing or fully open his mouth after undergoing a gruelling 12-hour surgery to remove a cancerous tumour from his mouth.

'My facial disfigurement from the surgery means I can't open my mouth wide enough for a strip of spaghetti, let alone to sing,' John detailed in an extract published in the Sydney Morning Herald .

'I can't get the movement to make the sounds I want to make, that's where the vibrations and my voice come from. It's a very disconcerting thing. And trying hurts.'

He said while he is still not yet able to belt out his trademark voice, he still has high hopes that he will one day be able to sing again.

'I was given a gift and to be able to get out there and affect people in some way was special, I would like to continue doing that. Though I am not putting all my hopes into it, we'll see,' he shared.

John also said he believes the tumour came about as a result of his long-term smoking habit, which he eventually managed to kick.

'Cancer doesn't discriminate, but as soon as I was told the results, I couldn't help thinking it was my own fault, I smoked very heavily all my life,' he said.

He said he started smoking at the age of 14 and would do so in secret after his disapproving parents once caught him.

His memoir has been co-written with Poppy Stockwell and will see Farnham tell his story in his own words and with his signature humour.

The book, slated for release on October 30, documents Farnham's early life and stardom growing up in Melbourne in the 1960s, to his comeback 1986 album Whispering Jack.

In August 2022, the hitmaker was shockingly diagnosed with oral cancer and then underwent a 12-hour surgery to remove the cancerous tumour.

During the operation, part of his jaw was also removed and he also had reconstructive surgery.

In a statement after his final surgery for mouth cancer, the music superstar said he was finally in the comfort of his own home surrounded by his loving family and felt like 'the luckiest man I know'.

'It's been a year since my first surgery and I've lost count as to how many other procedures there's been since then,' he said.

In August 2023, Farnham confirmed he was cancer-free and his son said he was doing 'really, really good' at the time.