Kieran Loveridge will spend at least three additional years behind bars for fatally punching Sydney teenager Thomas Kelly.

Loveridge was jailed in November for at least four years for the manslaughter of Mr Kelly in July 2012.

But that term was almost doubled in the NSW Supreme Court of Appeal on Friday, where Chief Justice Tom Bathurst declared Loveridge would serve a non-parole period of seven years for Mr Kelly’s death.

Mr Kelly, 18, suffered catastrophic head injuries after Loveridge punched him once in an unprovoked attack at Sydney’s red-light district, Kings Cross.

His life support was turned off two days later.

After community outrage over Loveridge’s four-year sentence, the DPP launched an appeal against the leniency of the decision, which was upheld on Friday.

Loveridge’s mother could be heard sobbing as she hurried from the court room.

The earliest her son can be released from jail is November 17, 2022.

Outside court, Mr Kelly’s younger brother spoke out for the first time.

Stuart Kelly, 16, pleaded for a change in community attitudes towards violence and responsibility.

“I want Thomas’s short life to have some meaning in his death, so that we can see change – a new fresh start,” he told reporters.

“I believe we should have respect for one another, for our friends, family, acquaintances, different cultures and complete strangers.

“A culture where we accept responsibility for our actions – not one where we all too often lay the blame on our past as an excuse for what we do today.”

Loveridge was also re-sentenced on Friday for his drunken attacks on four other young men on the same night he knocked Mr Kelly down.

He was sentenced to nine months jail for assaulting Matthew Serrao, 11 months for assaulting Rhyse Saliba, 13 months for assaulting Aden Gazi and at least 16 months for the assault occasioning actual bodily harm of Marco Compagnoni.

With time already served, Loveridge could languish behind bars until May 17, 2026.

A tearful Kathy Kelly said she felt the pain of losing her son every day.

“I think the thing that’s hardest for me to try to comprehend is that he lost his life for nothing,” she said.

“It wasn’t a grudge, it wasn’t domestic violence, although all those things are just terrible it’s just he died for no reason.

“That’s the thing we will never be able to comprehend.”

Justice Bathurst, on behalf of the full bench, spoke to the Kelly family’s “overwhelming grief” at the sudden loss of Mr Kelly as he handed down the new jail terms.

“He was doing nothing more than socialising with his friends in a public street when this terrible event occurred,” Justice Bathurst said.

Mr Kelly’s father Ralph said appealing the sentence had been stressful for the family.

“It shouldn’t be that the victims have to go through this … the offender should be given a sentence which is decent and let them appeal,” he said on Friday.

“Why should we have to go through this terrible stress over almost two years?”

He said he was touched by the acknowledgment of the family’s pain.

“But it’s never enough. You can’t bring him back,” Ralph Kelly said.

Public anger over Mr Kelly’s death and lobbying from the Kelly family led the NSW government to introduce a raft of new laws designed to tackle alcohol-fuelled violence.

Among the changes was the introduction of an eight-year minimum mandatory sentence for fatal one-punch assaults if alcohol or drugs are involved.