A Toronto couple recently pledged to donate $5 million to the Alzheimer Society of Toronto, the largest legacy gift the non-profit group has ever been promised to date.

Les and Marijane Dakens' generous, multimillion-dollar donation is part of the group's new "Leave a Legacy Education Series." The couple have long been committed to finding a cure for the chronic disease, which Les Dakens' mother suffered from for years before she passed away.

Dakens said he recalls watching his mother's memory slowly decline over the years. He said in the beginning stages, she would often forget where she had placed things in her kitchen. That forgetfulness, however, eventually developed into paranoia that strangers were trying to break into her house, and Dakens' mother was placed into a long-term care home.

"It was a very tough decision," said Dakens, who still gets emotional when thinking about moving his mother into a nursing home.

He said his father was struggling to take care of her at the time, and although it wasn't easy to watch his mother grow old in a home, it was the best decision in the end.

"The nursing care now is so good that it's the best thing for the patient," he said.

Across the city, more than 43,000 people are living with Alzheimer's disease or other forms of dementias, according to the Alzheimer Society of Toronto.

The Dakens' gift will be donated as part of their will.

"This is the largest gift in history that the Alzheimer Society of Toronto has ever received so for us, it's a huge deal," said Cathy Barrick, who heads the group. She said the donation will go toward research that will help find a cure for the disease.

With a report from CTV Toronto's Pauline Chan