Over and over again, Michel Francoise Theodoor Willemyns bludgeoned his younger brother with a spanner in an attack lasting hours.
Despite once having a loving relationship, Willemyns, 62, killed his sibling Patrick during a "hypomanic episode" in March 2017, occasionally filming the ordeal on his phone.
After practising swinging the spanner outside, Willemyns smashed his way into his only brother's residence west of Brisbane and attacked the 53-year-old chef as he lay on the couch.
He repeatedly hit his brother with the spanner and stomped on his head.
At times, father-of-two Willemyns stopped to talk to Patrick during the fatal assault, filming it on his phone.
"His injured brother did not respond intelligibly but groaned," crown prosecutor Matt LeGrand told Supreme Court.
The video footage lasting about 10 minutes was considered too distressing to be shown in court but was watched privately by Justice Melanie Hindman.
"The video is disturbing to say the least," she said.
It was unclear how many times Patrick was assaulted during the prolonged attack, the court heard.
Willemyns didn't leave the Karana Downs residence until about 5am - eight hours after his violent arrival.
The victim was later found with blunt force injuries all over his body, with 10 on his head alone.
Two blows were so severe they had fractured his skull.
Willemyns later told police his brother was "breathing and lucid" when he left.
"Whilst that is difficult to accept, if it is true it makes the crime even more horrific given the extent of the injuries that had been inflicted," Justice Hindman said.
"Patrick must have suffered terribly through the ordeal."
Barely 12 months earlier, Willemyns - formerly a respected university dean - was enjoying a "successful life", the court heard.
However it unravelled, along with his mental health, after his family returned to Australia from his university stint in Dubai.
His loving relationship with his brother then became "toxic" after their mother's death in late 2016.
He became paranoid his brother - head chef at Karana Downs Golf Club - would assault him and there was a dispute over money.
Five days before the attack, Willemyns went to a Brisbane police station claiming Patrick was harassing him and may have stolen his passport.
By the time he drove to his sibling's house in March 2017, Willemyns was in a "downward spiral", suffering an untreated mental illness while unemployed and homeless.
Defence barrister Catherine Morgan said there should be no difficulty concluding that Willemyns was in an abnormal state of mind at the time after his "bizarre" decision to record the ordeal.
She said his mental illness was so severe that after his 2017 arrest Willemyns was kept in a high-secure mental health facility for two years before stabilising under medication.
"He did not intend to kill his brother," Ms Morgan said.
"The person who misses Patrick Willemyns the most, the person who perhaps loved him the most, is sadly the man who killed him."
Willemyns was initially charged with murder but pleaded guilty to one count of manslaughter by reason of diminished responsibility.
"Good luck Mr Willemyns," Justice Hindman said after sentencing him to 10 years in jail.