Mark Potter and his partner Kelly had visited his sibling, David, at Harris Commercial Repairs Ltd in Essex on October 4, 2019.
The couple hoped to see a truck they were interested in buying.
Mark, 58, and David, 57, had planned to test-drive the vehicle together but, after waiting a few minutes for his brother to join him inside, Mark pulled off on his own.
He had failed to notice the other man standing in front of the lorry, and ended up fatally injuring him, Essex Coroner’s Court heard.
Mark tearfully told the jury: ‘I saw him in the mirror at the back of the vehicle. I lost sight of him then, I couldn’t see him in either of my mirrors.
‘I sat there for some time, I don’t know how long it was and I thought “just go (on the test drive) on your own”.
‘At that point I moved the vehicle forward.’
Mark explained that he would have been driving very slowly – at speeds below half-a-mile an hour.
He told the court he had heard David shouting and turned off the engine.
Mark continued: ‘I couldn’t see him, I didn’t know what it was. The last place I saw him was at the back, I went around to the back and he wasn’t there.
‘I went all the way around to the front and I saw his glasses and phone at the front. He was at the front of it.’
Realising what had happened, Mark immediately called an ambulance.
One of David’s colleagues, Graham Walsh, used a forklift truck to help lift the lorry so paramedics could have access.
A post-mortem examination revealed David had suffered traumatic chest injuries.
Mark was arrested by Essex Police but later released without charge.
Assistant coroner Tina Harrington said: ‘It’s particularly tragic in this case as one family member, the brother, was involved in an incident that involved his older brother.
‘[The family] have acted in a dignified way in what must have been, on occasion, extremely harrowing to have to listen to and to see.’
The Potter family said: ‘David was loved by everyone he met. He had a big, loving heart and always put a smile on your face.
‘He was the kind of person who would always put others first. The most warm and loving person you would ever meet, who lived life to the fullest with the people who meant most to him.
‘The best dad, husband, brother, stepdad and grandad who loved his family more than anything.’
Mark said he had been ‘excited’ to see David when he arrived at the site as it had been a while since they’d last seen each other.
They greeted with a ‘hug and kiss’ before the fateful test-drive took place.