It was at Christmas dinner in 2012 that Doc Neeson's family realised something was wrong with the enigmatic former frontman of veteran Australian rock band The Angels.

"You could see in his face and how he was talking that something wasn't quite right," recalls Neeson's son Keiran.

An ambulance rushed Neeson to Sydney's Royal North Shore Hospital where the 65-year-old singer had a seizure.

After a CAT scan, he was diagnosed with a high grade brain tumour and told that statistically, he had 18 months to live.

Plans for a national tour were put aside. Neeson's tumour was surgically removed and he began intensive rounds of radiotherapy and chemotherapy.

Neeson says he never planned to be a rock star. ( Supplied: Anna Bartle )

"It was a shock of course when somebody puts a use by date on me, but I still hung on to a shred of hope that I'd get back on the stage at some point," Neeson told Australian Story in a profile airing tonight on ABC1.

Neeson never planned to be a rock star. He wanted to be a teacher, or a film director.

He was in his last year of teachers' college in Adelaide when he was drafted into the army and his career direction shifted again.

Neeson was about to be posted to Vietnam as an infantryman when the military hierarchy realised he had a teaching qualification, and sent him instead to Papua New Guinea to teach the Pacific Island Regiment.

"Amazingly I got made up from a private to a sergeant. I rang my dad who'd spent 22 years in the British Army and he said I'd done in seven months what had taken him seven years," Neeson said.

Returning to Australia after military service, he took advantage of a Federal Government retraining scheme and enrolled at Flinders University to study filmmaking.

There he met a group of young musicians who would eventually form The Angels, the highest paid band in Australia by the late 1970s, with a string of big hits and the manic Neeson as lead singer.

Band goes electric after birth in the blues

In their earliest incarnation they were known as The Moonshine Jug and String band, an acoustic blues outfit with a strong Adelaide following.

When they decided to become an electric band, The Keystone Angels, audiences were not impressed.

"The crowds shrank from over 1,000 each night to just 200 in the space of about a week, because they weren't very good," says former band manager John Woodruff.

But it was a kind of apprenticeship for the band as they learned to play their instruments properly and to write original songs.

By 1976 they had changed their name to The Angels and released their first single, Am I Ever Going To See Your Face Again.

The song took off slowly but later became an unofficial anthem for generations of Australian youth.

Nobody is sure how it happened, but as the years passed, audiences began chanting their own X-rated response to the chorus.

Sorry, this video has expired The Angels perform Am I Ever Going To See Your Face Again

'Ribald' lyrics embarrassed General Peter Cosgrove in East Timor

When Neeson performed the song at the 1999 Tour of Duty concert for Australian troops in East Timor, it left Peter Cosgrove in an awkward position.

The man who is now Australia's newest Governor-General, was then commander of the INTERFET forces in East Timor and says he recalls the concert.

"I'm sitting up there with people like Jose Ramos Horta (East Timorese spokesman at the time) and Roman Catholic Bishop Belo of East Timor, overlooking the crowd and they had some alternative lyrics to Am I Ever Going to See Your Face Again," Mr Cosgrove said.

"I'll call them ribald lyrics.

"Bishop Belo leaned forward and said to me, 'Mr General, what are they singing?' And I said, 'Well Lord Bishop I really can't quite make it out'.

"Then Ramos Horta looked at me and I could tell that he could make it out!"

Musicians, fans rally for Neeson

Australian Story began following Neeson more than a year ago after the removal of his brain tumour and has been by his side during some memorable moments.

In April 2014, 2,000 fans crammed into Sydney's Enmore Theatre to see a fundraising concert for Neeson, featuring performances by his friends including Jimmy Barnes, Peter Garrett and Angry Anderson.

"When The Angels were big, we invested a lot of the money that we made into the band itself to try and go overseas again. So there was no kind of money salted away somewhere to fall back on," Neeson said.

Neeson receives an Order of Australia medal from NSW Governor Marie Bashir. ( Supplied )

"It's a pretty lean time at the moment."

Three weeks after the concert, Neeson was presented with an Order of Australia by NSW Governor Marie Bashir.

A MRI scan in February revealed the tumour in Neeson's brain had returned and may be life-threatening in the next three to six months.

"The news is grim, but some people can get through this, and that's the way I try to think about things," he said.

"So I'm looking forward optimistically to the future."

He has just released a new single, "Walking in the Rain" his first new recording in seven years.