At an 18th birthday party in country Victoria, Alexander Wells was driving around in a paddock with 10 people on the tray of his ute.
When the vehicle rolled, the youngsters were strewn across ground, and all but one of them survived.
William Grace, 16, was killed at the party at Gladysdale, east of Melbourne, in February 2017.
His mother, Donna Grace, got a call and rushed to the party in a state of panic and confusion.
She realised what had happened without being told.
"I could see police, a ute and someone lying on the ground, covered," Mrs Grace told the County Court on Tuesday.
"I recognised his shoes, so I knew it was William."
Police didn't let Mrs Grace near William's body at first, but she insisted on being by his side.
"I wanted to hold his hand," she said. "It was important for me to let him know I was there."
A friend soon led her away, and panic set in.
"I felt like I couldn't breath. They had to hold me up," she said.
A subsequent phone call to her husband, who was travelling for work, had been unbearable.
Mrs Grace spoke at a pre-sentence hearing for Wells, who has pleaded guilty to dangerous driving causing William's death.
Tears flowed in the courtroom, which was filled with family members of both William and Wells.
Mrs Grace said her son was an outgoing boy who had been a great support for her during her recent battle with breast cancer.
Craig Grace, William's father, said his son was his best friend.
"The loss of my son William has broken my heart," Mr Grace said.
"My grief and longing for my best mate is like a dark storm cloud that won't leave."
Mr Grace called for the judge to impose a weighty sentence on Wells to give his son justice.
"This was not a freak accident. An adult in control of a motor vehicle made the wrong choice and it ended in disaster," he said.
Wells driving remains unclear as some witnesses said he was doing a "donut" but others said he was simply turning.
Judge Paul Higham said the manoeuvre was "inherently dangerous" however it unfolded, given Wells was driving in a paddock with 10 people in the tray.
Defence lawyer Scott Johns SC said Wells had no prior criminal history and was sorry for his actions, but conceded a prison sentence was likely.
"This is a young man who, with everything going swimmingly in his life, errs this way and everything changes," Mr Scott said.
Wells, who also pleaded guilty to dangerous driving endangering life, remains on bail and will be sentenced on February 23.