The 29-year-old man charged in a crash north of Toronto that left three children and their grandfather dead was allegedly travelling at twice the speed limit at the time of the accident, a police sources told CTV News.

Marco Muzzo faces 18 charges as a result of a crash in Vaughan, Ont. on Sunday. Daniel, Harrison (Harry) and Milagros (Millie) Neville-Lake succumbed to injuries received in the three-vehicle crash. The children were aged nine, five and two.

Police sources say Muzzo was driving at least 120 km/h down Kirby Avenue -- a 60 km/h-road -- when he allegedly ran a stop sign and T-boned the minivan travelling down Kirby Road, which then hit a third vehicle. The allegations have not been proven in court.

The children’s 65-year-old grandfather, Gary Neville, was also killed in the accident.

Muzzo, who had just returned to Toronto from a bachelor party in Florida, has been charged with four counts each of impaired driving causing death, driving with a blood-alcohol level of over 80 (more than 80 milligrams of alcohol per 100 millilitres of blood) causing death and dangerous operation of a motor vehicle causing death.

He has also been charged with two counts each of impaired driving causing bodily harm, driving with a blood-alcohol level of over 80 causing bodily harm and dangerous operation of a motor vehicle causing bodily harm.

Sources told CTV Toronto's Tamara Cherry that Muzzo took two breath tests after the crash, and allegedly both times, blew more than twice the legal limit of 80 milligrams in both tests.

Muzzo is part of a family that owns a construction empire estimated to be worth more than $1 billion. The family owns Marel Contractors, based in Vaughan, Ont., which operates in Toronto, Ottawa, Calgary and southwestern Ontario.

He is set to appear in court on Friday.

With a report from Austin Delaney