A drunk and drugged learner driver who crashed while speeding without headlights is "deeply sorry" for causing the death of Cooper Ratten, the son of Hawthorn assistant coach Brett Ratten.
The 18-year-old - who was 17 at the time of the Yarra Glen smash - says he wishes he could change what happened last August.
Labelling the crash a "joyride that turned into a tragic accident", he said Cooper was greatly missed.
"I am deeply sorry and regret all the pain I have caused to your family through a foolish mistake," the teen told Cooper's family in a letter read out in court.
The teenager, who can't be named for legal reasons, appeared in court on Monday after pleading guilty to one count of culpable driving causing death.
He had a blood alcohol reading of 0.084 and ecstasy in his system when he failed to negotiate a bend and lost control of the speeding car about 3am on August 16, the court heard.
The car rolled end-over-end, ejecting 16-year-old Cooper from the back seat, throwing him about 65m from the wreck.
He wasn't wearing a seatbelt and died on the way to hospital.
His father, Brett Ratten, is the assistant coach at Hawthorn and was senior coach and captain at Carlton.
He wasn't in court but his wife - Cooper's stepmother - revealed the pain their family was suffering; particularly his younger siblings who often asked when their brother was coming home.
"We will never get to see where Cooper's life would have taken him," Joanne Ratten said.
"Our grief is beyond measurable."
Cooper's mother, Sharyn Ratten, said her family was broken.
"His shining light has blown out forever and left us in complete darkness," she said in a statement.
Collision experts believe the headlights were turned off and the car was travelling about 126km/h at the time the car crashed in "extremely foggy" conditions.
But the teenage driver, who suffered fractured vertebrae in the smash, did not accept he was travelling that fast, his barrister said.
The 18-year-old, who has no criminal history, has received abusive messages over social media.
He drank at a friend's place on the night of the crash before going to a Yarra Glen football club function where he hid and continued to drink in secret.
He went back to his friend's home and got behind the wheel, after twice being warned not to.
The teen's plea hearing continues on Tuesday.