Marlo Thomas and Phil Donahue's marriage was founded on "love, listening, and lust."

Marlo Thomas and Phil Donahue's marriage, which spanned over four decades, ended with his death on Sunday at the age of 88.

Thomas posted a tribute to her late husband of 44 years on Instagram, along with a cherished photo of the couple.

Thomas wrote, "I'm sure you've heard the sad news that I lost my sweetheart last night, so I understand that I'll be stepping away from this page for a while to take care of myself and the many people who took care of Phil and held him close to their hearts."

She thanked everyone for the "beautiful messages of love and support" and "generous way" they allowed her and Phil to share their life adventure with them.

"Phil, a man who spent his career entertaining audiences, found great joy in our community and would be deeply moved by the heartfelt thoughts and memories shared here."

Marlo wrote, "Until I come back, I hope you have good health and happy days with loved ones. Keep those you cherish close, just as I did with my dear Phillip. Love, Thomas."

Their marriage, which they kept private for many years, is now something they are happy to share with others.

Last May, People reported that Thomas attributed their marital success to three "Ls" in their relationship.

She revealed to the outlet at the Women In Media Foundation's 48th annual Gracie Awards Gala that she refers to it as the three Ls: love, listening, and lust.

"The three L's are listening, loving, and lacking lust."

The 'Friends' star joyfully declared, 'He's the best and I'm incredibly fortunate.'

In 1977, Donahue and Thomas first crossed paths on "The Phil Donahue Show," and it was evident to all who watched and listened that there was a special bond between them.

Several people, including Thomas, contacted him and inquired about the interview, including a neighbor of Donahue's.

""It was evident, but we didn't realize it then," he remarked."

The next day, Thomas asked her out after calling her, and that was it.

Thomas and Donahue had a long-distance relationship, with Thomas residing in Los Angeles and Donahue in Winnetka, Ill.

"Love, listening and lust. You have to listen, and then you'll know what the other person is really thinking and going through. … And without lust, you don't have anything." — Marlo Thomas

"Thomas shared with the New York Times in 2023 that Phil had told him he couldn't live in L.A. and didn't want to spend the rest of his life interviewing John Wayne. Thomas responded by saying he could live in New York or L.A., and ultimately, they decided on New York."

Donahue had previously been married and was a father to five children, while Thomas had never been married and had no children up to that point.

In 2011, Thomas stated to AARP Magazine that he would not attempt to act as a traditional mother to Phil's children but instead would be their friend.

The friendships I established with them are as strong today as they were 30 years ago — even stronger.

The couple married in 1980, but not without some last-minute hesitations.

In an interview with Planet Chronicle Digital in 2020, Thomas revealed that they had already separated three months prior to their wedding.

The "That Girl" star remembered how they were frequently arguing due to living and working in different cities, making compromises to accommodate two full and different lives. Additionally, Phil faced the pressure of raising his four sons alone. Eventually, both of them realized they couldn't continue and broke up.

"I started dating Phil, but I got back together with an old boyfriend. Despite being miserable, all I could think about was Phil. Then, one night, I received a call from Phil, who said, "I never thought anyone could be this irreplaceable." We got married 12 weeks later."

In a 2023 interview with People, Thomas revealed that on her wedding day, she was running late getting ready at her parents' house where the ceremony was taking place. She admitted to her father that she was scared because she never wanted to get married. He advised her not to go through with it if she wasn't sure.

She left the room to walk down the aisle with her father and realized something.

"As I walked down my parents' living room aisle, I saw Phil standing there with his hands like an altar boy, and I thought it was just him. What was I so scared of? she wondered. It was just him, and that was it."

Despite their happiness and love following their marriage, Thomas and Donahue kept their relationship private and away from the public eye.

Donahue and Thomas stated in 2020 to Planet Chronicle Digital that they were grateful that their paths crossed and they decided to spend the rest of their days together. That moment was and still is sacred to them, and they wanted to safeguard it.

In the same year as their 40th wedding anniversary, they published a book titled "What Makes a Marriage Last: 40 Famous Couples Share Their Keys to a Successful Life."

In 2020, the couple revealed to AARP magazine that they had always kept their projects separate as an "ironclad rule of our marriage."

The couple started their exploration of relationships through their book and podcast, "Date Night," where they interviewed famous long-lasting couples and provided advice for all.

They agreed that the key to a successful marriage lies in the fact that there is no one secret formula. Instead, it involves a multitude of factors.

"Our secret will be revealed in the book, but one thing is certain: once we committed to each other, we vowed to never seek an escape route, even during tough times," they stated.