Parents woken after son involved in fatal brawl on their doorstep

The parents of a Queensland teenager have testified that they were woken up by the aftermath of their son's alleged fatal stabbing just metres from their front door.

Balin Stewart was aged 16 when his heart was pierced by a 12 centimetre steak knife blade on January 20 last year outside his family's home in the Sunshine Coast suburb of Buddina.

A male aged under 18 at the time of the alleged incident, who cannot be identified for legal reasons, pleaded not guilty to murder in the Brisbane Supreme Court on Monday.

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Crown prosecutor Rebecca Marks said the defendant attacked Balin out of jealousy because he was spending time with the teenager's ex-girlfriend.

"He stabbed (Balin) with a purposeful motion ... in one of the most vulnerable areas in the human body and immediately before he did so, (said) he wanted to kill him," Marks said.

Balin's mother Kerri-Lyn and father Michael gave evidence on the first day of the trial.

Kerri-Lyn said on the evening of January 20 Balin and some friends, including a girl who he had been in a relationship with a few years ago and who had broken up with the defendant about six months beforehand, were hanging out at home before going to a party.

The group of teenagers returned about 10.30pm and Kerri-Lyn said she told them to keep the noise down before she went to bed.

"I went to sleep and the next thing I knew, I heard (the defendant's ex-girlfriend) banging on my window saying 'come outside, come outside'," Kerri-Lyn said.

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Kerri-Lynn said she ran out the front door when the girl told her Ballin had been stabbed and found him unconscious and the defendant saying, "I'm sorry, I'm sorry, I can't believe I did that".

"I called the ambulance and said my son had been stabbed," she said.

Balin was pronounced dead at 11.50pm after his parents, neighbours, police and paramedics attempted to revive him.

Under cross examination from barrister Charlotte Smith, Kerri-Lyn said it was possible the defendant had also said "I didn't mean it".

Michael testified he was initially less worried after looking at this son's chest wound, which was only 1cm to 2cm wide.

"There was not a lot of blood and it didn't look not as bad as I first thought. I later learned that this was because it hit his heart," he said.

The jury was later shown a video of a police conversation with the girl who had been romantically involved with Balin and the defendant.

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The girl, who cannot be named for legal reasons, said she and Balin decided to make and send provocative videos, which suggested they had resumed a relationship, to the defendant.

The defendant responded by saying he had driven to Balin's home and dared him to come outside.

The girl said the defendant punched Balin, pulled out a knife and said he was going to kill him.

"(Balin) fell to the floor. I didn't know he stabbed him. I was so confused," the girl said.