The father of a teenage water polo player killed in an allegedly unprovoked, one-punch attack in Brisbane's Fortitude Valley has remembered his son as a "brave young man".

Key points: Cole Miller, 18, dies after one-punch attack in Fortitude Valley early Sunday morning

Cole Miller, 18, dies after one-punch attack in Fortitude Valley early Sunday morning Two 21-year-old men charged with unlawful striking causing death

Two 21-year-old men charged with unlawful striking causing death Mr Miller's father describes son as a "beautiful, brave young man"

Cole Miller, 18, was knocked unconscious on Duncan Street in Fortitude Valley in Brisbane's entertainment precinct about 3:35am on Sunday after a night out on the town.

Police said he was struck once in the back of the head and hit the pavement, leaving him with serious injuries.

He was taken to Royal Brisbane and Women's Hospital in a life-threatening condition.

On Monday afternoon, police confirmed he had died.

Armstrong Renata and Daniel Maxwell, both 21, faced Brisbane Magistrates Court on Monday charged with grievous bodily harm over the assault.

Those charges were then upgraded to unlawful striking causing death, following Mr Miller's death.

The charge, which was introduced in 2014 as part of Safe Night Out legislation, carries a maximum penalty of life imprisonment.

Mr Miller's father, Steven, gave a brief statement to the media.

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"Cole was a beautiful, brave young man with his whole life yet to be lived," he said.

"Our family and many close friends have been by his bedside since the incident."

He thanked both the community and emergency services workers for their support.

"The Miller family would like to sincerely thank the support provided by Cole's school friends from Brisbane State High, the water polo community and the many, many, many others who have sent messages of love and hope," he said.

Earlier, the court heard Maxwell approached Mr Miller and his friend and asked them if they wanted to fight before Renata allegedly punched Mr Miller in the head.

Both were remanded in custody and will appear in court on Tuesday.

Speaking to the media, Queensland Attorney-General Yvette D'Ath described Mr Miller's death as a "senseless tragedy".

Unlawful striking charge explained "Unlawful striking causing death" is defined as hitting another person on the head or neck and subsequently causing the death of that person

"Unlawful striking causing death" is defined as hitting another person on the head or neck and subsequently causing the death of that person It was added as a new offence in the Queensland Criminal Code in 2014 as part of a suite of measures introduced in the Safe Night Out Legislation Amendment Bill

It was added as a new offence in the Queensland Criminal Code in 2014 as part of a suite of measures introduced in the Safe Night Out Legislation Amendment Bill The charge "fills the gap" between manslaughter and an assault that results in the death of a person

The charge "fills the gap" between manslaughter and an assault that results in the death of a person The Queensland Government's Safe Night Out laws are aimed at reducing alcohol and drug-related violence in the state's nightlife Source: Quinn & Scattini Lawyers/Queensland Government

"No parent ever wants to get the news about their child dying, and dying at the hands of a violent incident," she said.

"I say our thoughts and prayers go out to the Miller family right now."

Acting Premier Jackie Trad said Mr Miller's death highlighted the need for new alcohol-fuelled violence laws.

"My thoughts go to the family of this young man. It's just awful to think a son who is just on the brink of becoming an adult has been injured so traumatically and unnecessarily," she said.

"It really does speak to the fact this Government has decided to take very seriously stamping out this sort of senseless drunken violence.

"We will be moving ahead with our alcohol-fuelled violence laws later on this year."

Tributes flow for 'talented' sportsman

Mourners lay flowers at a vigil for Cole Miller in Chinatown, Brisbane. ( ABC News: David Lewis )

Dozens of mourners gathered in Brisbane's Chinatown just after 6:00pm to lay flowers in memory of Mr Miller.

Chris Owen, the first responder from Night Watch who tried to save the teen's life on Sunday, said Mr Miller's death was a terrible tragedy.

"We come out here to try and stop this kind of thing from happening and when you're not able to do that, that's always a hard thing to deal with," he said.

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Tributes for Mr Miller have also flowed on social media, led by a heartfelt post from his former water polo team, the Brisbane Barracudas.

"Cole Miller was in the prime of his life, a talented young water polo player reaping the rewards of his hard work and dedication to the sport he loved," the post read.

"This was his second season playing at the elite level with the National League and he had a promising career ahead of him.

"Our thoughts and prayers are with the Miller family."

Mr Miller was out with a teammate on the night he was attacked. They were taking a break from their busy training schedule.

He was due to travel to Adelaide to compete at the national championships on Thursday.

Friends of Mr Miller also took to Twitter to send their messages of support, tweeting with the hashtag #ripcole.