The 73-year-old underwent a 12-hour operation in August to remove a cancerous growth from his mouth.

On Monday, the singer's sons Rob, 41, and James, 34, thanked his fans for their support and well wishes following his diagnosis.

"We thank everyone who took the time to write a lot of these amazing messages to us," Rob told A Current Affair.

"It was kind of comforting to know that Australia was behind him, I know that he appreciated that, I remember when we first told him, he got teary," James said.

"He never expect everyone to still love him. It was nice for him to hear that, thank you everyone."

The boys spent every day following Farnham's surgery at his bedside and said they are not even thinking about whether he will sing again.

"There's a long way to go, It's definitely not on his mind. He just wants to get better," Rob said.

Now in a rehabilitation facility, Farnham is finding his audience meeting new nurses on the ward daily and cracking jokes, according to his sons.

But it would've all fallen apart if not for Jill, his wife of 49 years, James said.

"She is an amazing woman, and has been strong through this whole thing and held us together at times," Rob said.

Before his surgery, Farnham said a cancer diagnosis was something many people faced each day "and countless others have walked this path before me".

His diagnosis came three years after he suffered a health scare and was hospitalised with a severe kidney infection.

Farnham shot to the top of the charts with his 1986 album Whispering Jack.

It produced one of the nation's best-known anthems, You're the Voice, and propelled Farnham to hero status.

Australian Associated Press