The relationship began during the COVID-19 pandemic, Tory said, during a time when he was regularly away from his wife of more than 40 years.
The mayor told the press that the extramarital affair "ended mutually by consent this year."
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"I am deeply sorry, and I apologize unreservedly to the people of Toronto, and to all of those hurt by my actions," Tory said in his statement. "Most of all, I apologize to my wife, Barb and to my family who I've let down more than anyone else."
Tory was elected as mayor of Toronto in 2014. He was re-elected in 2018 and won again in 2022.
"I deeply regret having to step away from a job that I love in a city that I love even more," Tory said. "I believe, in my heart, it is best to fully commit myself to the work that is required to repair these most important relationships as well."