Marlo Thomas has the keys to a long-lasting marriage.

In an interview with People at the Women In Media Foundation’s 48th Annual Gracie Awards Gala, she revealed what makes her 43-year marriage to Phil Donahue last.

"I call it the three Ls. Love, listening, and lust," she said.

"Those are the three L's. You have to listen and then you'll know what the other person is really thinking and going through. You have to love each other. And without lust, you don't have anything."

The "Friends" star also happily told the outlet, "He’s the best. I’m very lucky."

Phil Donahue and Marlo Thomas posing together

Phil Donahue and Marlo Thomas have been married 43 years. (Dimitrios Kambouris)

MARLO THOMAS DOESN'T JUST WANT TO BE REMEMBERED AS 'THAT GIRL' DESPITE SHOW'S LASTING SUCCESS, BOOK REVEALS

The couple tied the knot on May 21, 1980, but kept things low-key for this year’s anniversary.

"Well, it was just fun just to be alone," Thomas said. "Sometimes we've given parties and done things, but we just felt like this year we wanted to just hang out alone. Go to the theater, go to dinner, walk down the street, just be together. It was great."

The "That Girl" star first met Donahue when she was a guest on his talk show, "The Phil Donahue Show" in 1977.

In 2020, the couple released a book near their 40th anniversary titled, "What Makes Marriage Last: 40 Celebrated Couples Share with Us the Secrets to a Happy Life."

They spent nine months speaking with celebrity couples whose relationships they’ve admired over the years, like Kevin Bacon and Kyra Sedgwick, Ron and Cheryl Howard, and Chip and Joanna Gaines.

Phil Donahue and Marlo Thomas stand together at the Paley Center

In 2020, Donahue and Thomas released a book about relationships and marriage, titled "What Makes Marriage Last: 40 Celebrated Couples Share with Us the Secrets to a Happy Life." (Mark Sagliocco/FilmMagic)

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Thomas and Donahue spoke with Fox News Digital at the time about the project, noting that it was one of the few times they’d spoken so publicly about their relationship.

"The way we saw it, we were very lucky that our paths crossed when they did, and that we’d made the decision to spend the rest of our days together," Thomas and Donahue said. "That was — and remains — sacred ground to us, and we wanted to protect it." 

Phil Donahue in a tuxedo and Marlo Thomas in a black gown together on red carpet.

In a recent interview, Thomas described the three Ls that help their marriage last, "Love, listening, lust." (Steve Granitz/WireImage)

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The couple shared this insight into what’s helped their marriage last four decades.

"As for our secret, you’ll get pretty good glimpses of it in the book — but one thing for sure is that, once we decided to commit to each other, we also decided that no matter how tough things might get, we would never look for an escape route."