Jeff Daniels and wife Kathleen Treado wed in 1979
Kathleen Treado and Jeff Daniels
Credit: Taylor Hill/FilmMagic

Jeff Daniels is sharing his secret to a successful marriage. 

The American Rust star, 66, has been married to high school sweetheart Kathleen Treado since 1979. They have three children together: Ben, 37, Lucas, 34, and Nellie, 30, as well as three grandchildren and another on the way. 

As for what makes their 42-year marriage work, Daniels told Today the key is "understanding that mansplaining is a real thing." 

"It probably qualifies as a disease," he said during his appearance on the morning news show Friday. "And you should get the suitable medication." 

Daniels added, "That's the key to mansplaining is, just don't speak as much, and you'll probably last long."

The actor also shared that two of his grandchildren dressed up as the characters from his 1994 movie Dumb and Dumber for Halloween last weekend.

"I loved it," he told Today of the costumes. 

Daniels and Treado reside in their home state of Michigan, where they moved from New York City in 1986

Back in 2019, Daniels told PEOPLE the move was meant "to create as much a sense of normalcy as possible," amid his rising fame. 

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Kathleen Treado and Jeff Daniels
Kathleen Treado and Jeff Daniels in 1996
| Credit: Evan Agostini/Liaison/Getty

"It was a very dramatic move in 1986 to move to Michigan, but that was to keep the family number one. And that worked," the Emmy winner said at the time. 

"Kathleen's permanent. The family's permanent," he continued. "Careers are job to job, you're hot, you're not."

Daniels, who recently returned to Broadway to reprise his Tony-nominated role in To Kill a Mockingbird and is preparing for the season finale of American Rust, added that he never "bought" into fame. 

"I knew how fleeting it was and I didn't trust it for a second, so I moved to Michigan," he said.