A Sydney man who fatally bashed the son of rock singer Angry Anderson while high on drugs has been sentenced to eight years in prison.

Mathew Flame was last month found guilty by a jury of the manslaughter of Liam Anderson in a Northern Beaches park in 2018.

Flame had mixed alcohol, cannabis and up to 10 MDMA capsules during a night out in Darlinghurst and at friends’ houses.

He was acquitted of a murder charge on mental health grounds after claiming to have been hallucinating that his 26-year-old friend was a demon trying to kill him.

In sentencing, Justice Richard Button found Liam’s death was “extended, gruelling, terrifying and horrifically painful”, and Flame bitterly regretted his actions.

“Those emotions will be with him for the rest of his life,” he told the NSW Supreme Court in Sydney.

He will be eligible for parole in May 2024.

Rock legend Gary “Angry” Anderson and his youngest son Liam. Photo: ABC/Facebook

Justice Button warned Flame he may be held in custody after his full sentence expired if he is considered a risk to the community.

Flame started taking MDMA at festivals as a 15-year-old and had experienced similar demonic hallucinations in the months before the incident, his trial heard.

He was diagnosed with schizophrenia after the attack, but his lawyers argued the 22-year-old was not criminally responsible for murder because the chronic illness was underlying at the time.

However, Justice Button today found mental illness did not substantially contribute to the homicide, but the psychoactive drugs operated on a vulnerability to it.

He said the case was an example of the “unforeseen and unintended ruin” brought upon many lives by the use of prohibited drugs.

The judge noted Flame was “eager” to receive treatment in custody and has the support of his family, but must avoid psychoactive substances for the rest of his life.

Flame nodded in the dock.

Outside court, Angry Anderson said his son had his life taken away from him.

“Two years ago, my family and those that love him started a lifetime sentence,” he said.

Flame’s lawyer Leonie Gittani said her client had a long road ahead of him with his rehabilitation, but said she had “every faith” he would become “an upstanding member of the community” once released.

“He’s devastated,” she said.

“It was a close friend. It was his best friend. He has to live with that for the rest of his life.”

Last week, Angry Anderson told the court he had been “condemned to a life of sadness” following his son’s death.

“When he died part of me died with him,” the Rose Tattoo singer said.

Liam’s mother, Lindy Anderson, who hugged Flame on the day of the verdict, said she had forgiven him because it was a way for her to find peace.

“I choose to forgive because the poison of anger will only eat me away,” she said.

Flame’s trial heard the apprentice plumber showed no emotion as he “stomped” on Liam, who was trying to help him when they ended up alone in a Queenscliff park.

He was ranting about Satan when he was arrested and told police he was “tripping out” and had “lost his mind”.

–ABC