Christopher John Adcock, 39, pleaded guilty in the Brisbane Supreme Court on Friday to the unlawful striking causing the death of his 30-year-old brother Darren Adcock.

Tensions between the brothers had been simmering weeks before the fatal assault on March 11, 2021, in Landsborough, north of Brisbane.

Adcock was furious after Darren had borrowed money, never paying it back, and blocked him on social media.

Before they were both invited to their niece’s eighth birthday party, he warned family members he planned to “punch Darren in the head” to teach him a lesson.

He tried to corner Darren at the party, but his younger brother ignored him and tried to walk away.

Adcock was enraged.

He attacked from behind, launching a single blow to his head, causing him to lose consciousness and hit his head on a concrete footpath as he collapsed.

The father of two’s skull was fractured and he suffered significant bleeding on the brain.

He would never regain consciousness and died in palliate care on April 3.

His family gave heartbreaking impact statements, telling Adcock he had destroyed their lives.

“The loss of a child is unbearable, and I have lost two sons,” the pair’s mother said in a statement read to the court.

“You caused all of this. You have robbed Darren of life and love and never being able to see his sons grow up.

“We are broken and empty … and you are the one who caused it all.”

Adcock remained impassive as his family’s grief was laid bare in court, refusing to look at them.

Defence lawyers said Adcock pleaded guilty at the earliest opportunity to spare his family further heartbreak.

Justice David Boddice warned Adcock that he would have to live with the knowledge that he killed his brother in an act of “senseless and gratuitous violence”.

“It is inexplicable. For reasons that seem to be nothing at all, you approached your brother from behind and struck him,” Justice Boddice said

He sentenced Adcock to 10 years imprisonment, ordering he must serve at least 80 per cent before being eligible for parole.