A family from Timmins, Ont., was sitting down for their usual Monday morning breakfast when they discovered their cereal box was a piece of Canadian history.

The Gaudette family was preparing to start the day when they reached for an unopened box of Frosted Flakes. Turns out, it was the last box of cereal produced at the now-shuttered Kellogg’s plant in London, Ont.

“I noticed there was something written on the plastic bag inside after I opened up the box,” Stephane Gaudette told CTV News.

Written in black marker and dated Dec. 5, 2014, the note read: “This is the very last bag of Canadian cereal for the Canadian market from Kellogg’s London Ontario plant.”

The message was written by three long-time workers at the 138-year-old plant, which closed in December.

The men wrote their names and included what is presumably the number of years they each worked at the plant: 24, 28 and 29 years.

Gaudette recognized the historical significance of his find.

“I found it kind of sad, because I knew it was a major employer in London,” Gaudette said. “My heart went out to these people and I knew it that it had a long, rich history.”

Former Kellogg’s workers in London say they know exactly what the message meant, and who wrote it.

“This wasn’t meant to be done as a joke; these are three fellas that took a lot of pride in their work and they wanted to be there on that final day and put out that final box,” said Mike Coulter, a former Kellogg’s employee.

In December 2013, Kellogg's announced the plant was closing within a year and its cereal production was being moved to a newer facility. The closure put 450 people out of work.

Gaudette, a history teacher, said he doesn’t yet know the final fate of the cereal box, but he is planning to show it to his students.

With a report from CTV News London