Colleagues of an off-duty police officer killed in a two-car collision north of Toronto are remembering their fellow officer as a positive person undaunted by setbacks.

York Regional Police Supt. Mark Grant died Thursday afternoon when a pickup truck collided with his unmarked police car on a rural road in Uxbridge, 45 minutes northeast of Toronto.

"He was a true leader at York Regional Police, a consummate professional, hardworking and extremely dedicated," said York Police Chief Eric Jolliffe.

The crash occurred near the intersection of Sanford Road and the York-Durham Line.

Grant and his fiancée, both 54, were returning from a police conference in Chicago at the time of the crash.

Emergency crews pronounced Grant dead at the scene, while his fiancée was transported to hospital where she remains in serious but stable condition.

Durham Regional Police continue to piece together the details of the fatal crash, but believe the 76-year-old driver of the pickup truck may have run a stop sign. That driver suffered minor injuries.

The accident occurred just miles from where York Police Const. Garrett Styles was dragged to his death by an under aged driver four months ago. The lawyer of the accused youth said Friday that his client intends to plead not guilty.

"I don't think it's a surprise to anyone standing here that this police service has had a tough year," Jolliffe said.

Police said that Grant's death is classified as an "on duty death while carrying out an administrative role," as opposed to being killed in the line of duty. This could determine whether he would be honoured with the pomp of a large police funeral.

Markham Mayor Frank Scarpitti offered his condolences to the police force on Friday as well as to Grant's family and friends.

"Supt. Grant was an exemplary officer whose commitment and passion for his work were well known throughout the force and the region," Scarpitti said in a statement.

"This invaluable member of York Regional Police Services and our community will be greatly missed."

Grant began his career with YRP in August 1979. The 32-year veteran was promoted to the rank of Sergeant a few years later.

The upbeat officer moved through several roles during his three decades with the police service. He worked as a detective, patrol supervisor and led a team of drug investigators with York's morality bureau.

In 2000, Grant received the Governor-General's Police Exemplary Service Medal. He received a similar honour again in 2010.

Grant was promoted to Superintendent in June 2010, the role that would become his last rank with the YRP.

"It's a very difficult situation for our organization to deal with and I know people are all suffering today because of his loss," said York deputy police chief Bruce Herridge.

With a report from CTV Toronto's Tamara Cherry