Doris Day, one of the most famous stars to come out of Hollywood, left it all behind in 1973 — and she never looked back.

The perennial girl-next-door whose career as a singer and actress spanned almost 50 years and made her one of the most popular entertainers in the United States passed away early Monday at 97.

But what prompted America’s sweetheart to ditch the spotlight in her early 50s? Day herself once gave an explanation in a 2011 interview with People magazine.

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Doris Day after receiving the Cecil B. DeMille Award on Jan. 28, 1989. (AP Photo, File)

“I really loved being there, but then I started to notice that it was changing,” Day recalled about Hollywood. “It really started to change, and, oh, people were moving away because strangers from foreign countries were all over on the street and tearing the beautiful houses down and putting up boxes. I really wasn’t happy about that at all. Wasn’t the town I knew.”

At the time, Day admitted that she hadn’t “thought much about” a Hollywood comeback. However, she didn’t completely rule out the possibility.

“But I wonder if I would, you never know,” she said. “You never know about me, and I never know about me! If I hadn’t stayed in LA, I might play a grandmother in a movie, who knows.”

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In this Jan. 6, 1976 file photo, actress and singer Doris Day answers questions in New York, during an interview on the book "Doris Day: Her Own Story," written by A.E. Hotchner. The star spent her final years dedicating her life to animals in need. (AP)

According to the outlet, Day instead chose to focus on her love of animals and became a tireless activist, ultimately leading her to establish the Doris Day Animal Foundation in 1978.

And when Day was asked what life has taught her over the years, she shared, “To live it to the fullest, your best.”

“Live it, and have fun, enjoy each day,” she continued. “You know, it’s not coming back again and enjoy each day. I’m looking out and the sun is shining and it’s so pretty in the garden, what’s not to love?”

Back in 2017, Day’s business manager and close friend Bob Bashara told Fox News that Day stayed busy pursuing her lifelong passion.

Doris Day signs her name in cement by her handprints on Jan. 19, 1961 on Hollywood Boulevard, Hollywood, California. (Photo by Hulton Archive/Getty Images)

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“When she left Los Angeles, she moved to Carmel. The main reason was she wanted to focus on animal rescue,” Bashara told Fox News. “She was already rescuing animals in Beverly Hills.

"They called her the Dog Catcher of Beverly Hills because she’d be on her bike riding around Beverly Hills and if she saw a stray, she would try to find it a home. And if she couldn’t, she’d take it home and get it rehabilitated. But she would keep it herself a lot of times. But she really couldn’t do what she wanted to do concerning animal welfare in Beverly Hills.”

Bashara claimed those who knew Day best wouldn’t be surprised by her decision. In fact, Day’s determination to rescue animals started long before she found fame.

Doris Day once revealed she had no regrets leaving Hollywood behind. (Getty)

“She found a piece of property in Carmel Valley and she found a home there that she renovated and restructured to a facility where she could house animals,” said Bashara at the time. “She was out picking up animals, people were leaving them at the door. If an animal needed to be adopted, she would go to the homes first and made sure it was a good environment for the animal before she would let the people have it.”

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After the star launched the Doris Day Pet Foundation, she then formed the non-profit organization Doris Day Animal League to tackle animal overpopulation. Bashara said it’s still in operation today and has merged with the Humane Society of the United States.

“She lives in California on the same property,” he said. “She can’t really go out and rescue animals. But people still leave them on the doorsteps. Or if a feral cat wanders on the property, she’s bound to take it in and care for it. Someone even left an animal outside her gate in a box because they knew she would care for it. She still looks for organizations that her foundation can give money to and rescue animals.”

In this Feb. 26, 1958 file photo, actress Doris Day, center, Tony Curtis, right, and Buddy Adler pose with their awards presented to them by the Hollywood Foreign Press Association at its annual awards dinner in the Cocoanut Grove in Los Angeles. — AP

Over the years, Day was asked to come out of retirement and scripts came her way. And while she was not interested in returning to the spotlight, Day didn’t completely give up on her love for music.

“She loves singing,” Bashara said at the time. “She sings around the house a lot and her voice is terrific. We keep telling her she could record again if she wanted to. But she’ll say, ‘Oh, I’m rusty.”

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But despite her lasting success, Day was perfectly content focusing on rescuing animals and had zero plans to slow down.

“She’s said this before… she never really wanted to be a movie star,” said Bashara. “She wanted to get married, have a family… She loves living the simple life. I don’t think she was ever really interested in the celebrity side of it. She wanted to work with animals and she wanted to do that in a more private setting.”

Fox News' Sasha Savitsky contributed to this report.