One of the two men accused of a fatal attack on Cole Miller is "very stressed" and "very anxious" after his charge was upgraded to one that carries a maximum sentence of life in prison.

Key points: Cole Miller, 18, died in hospital on Monday morning after an alleged random attack in Fortitude Valley the day prior

Cole Miller, 18, died in hospital on Monday morning after an alleged random attack in Fortitude Valley the day prior Accused attackers Daniel Jermaine Lee Maxwell and Armstrong Renata have charges upgraded from grievous bodily harm to unlawful striking causing death

Accused attackers Daniel Jermaine Lee Maxwell and Armstrong Renata have charges upgraded from grievous bodily harm to unlawful striking causing death The 21-year-olds face a maximum penalty of life imprisonment if found guilty

Daniel Jermaine Lee Maxwell and Armstrong Renata, both 21, have been remanded in custody after a previous charge for grievous bodily harm was upgraded to unlawful striking causing death.

Mr Miller, 18, died in the Royal Brisbane and Women's Hospital on Monday morning, more than 24 hours after being hit once in the back of the head in an alleged random attack in Fortitude Valley in Brisbane's entertainment precinct.

The talented Brisbane Barracudas water polo player and former Brisbane State High School student never regained consciousness after the attack.

Renata, from Coombabah on the Gold Coast, sat slumped over in the Brisbane Magistrates Court. He did not speak and made no application for bail.

The matter was adjourned until February 8.

Maxwell, from Tanah Merah in Logan, appeared about an hour later. He too made no application for bail and his case was adjourned until later this month.

Outside court, lawyer Neil Lawler said Renata was very distressed.

"He's very stressed, very anxious, he's never been in custody before and the watch house is pretty tough place," he said.

"It's a very, pretty serious charge, it carries a life imprisonment with at least 80 per cent to be served. I think it's safe to say it's a tragedy for all involved."

He said they may make a bail application at a later date.

"We are going to obtain some police material and perhaps make a bail application," Mr Lawler said.

Maxwell's lawyer Michael Boscher said his client was out celebrating his 21st birthday on the night of the incident.

"He feels nothing but the greatest sympathy for the victim's family, he's only a young man himself, it was his birthday on the evening in question," he said.

"He's got no family or friends really here in Australia, they're all in New Zealand, so obviously he's doing it tough."

Mr Boscher said his client would apply for bail at a later date.

Cole Miller played water polo for the Brisbane Barracudas. ( Supplied )

Thousands plan to gather to support Miller family

On Monday night, dozens of mourners attended a vigil in Fortitude Valley to lay flowers and remember Mr Miller.

Friends have also taken to social media, with the Facebook page RIP Cole Miller attracting more than 1,200 followers in less than a day.

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

More than 3,500 people have also registered their interest to attend an event at King George Square in the Brisbane CBD on Monday, January 11 to remember Mr Miller.

Mr Miller's father Steven gave a brief statement to media yesterday, remembering him as a "brave young man".

"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.

A lifelong love of water polo

Mr Miller, originally from the Sunshine Coast, had been involved in water polo for most of his life.

He trained at the Mooloolaba Surf Life Saving Club and previously worked at the Kawana Aquatic Centre, which his father still helps to run.

Mr Miller was in his second season with the national water polo league at the time of his death.

Waterpolo Australia CEO Christopher Harrison yesterday tweeted Mr Miller's passing was "a dark day for our sport".

Mr Miller is the younger brother of Australian water polo player and Olympian Billy Miller.

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