(CNN) Doris Day, the box-office queen and singing star whose wholesome, all-American image belied an often-turbulent personal life, has died, her foundation announced Monday.

She was 97.

The actress passed away early Monday surrounded by a few close friends at her Carmel Valley home in California, according to the Doris Day Animal Foundation

She had just celebrated her 97th birthday last month with nearly 300 fans who gathered in Carmel.

Day recently contracted a serious case of pneumonia that resulted in her death, the foundation said.

Day was arguably the top female box-office star in Hollywood history, with a No. 1 ranking in 1960, 1962, 1963 and 1964. She had her first hit as a big-band vocalist during World War II before making nearly 40 movies in the next two decades, reigning supreme at a time when her contemporaries included Audrey Hepburn, Marilyn Monroe and Elizabeth Taylor.

Doris Day teamed up with Rock Hudson in three romantic comedies in the late '50s and early '60s.

Sex comedies such as "Pillow Talk," "Lover Come Back" and "That Touch of Mink" established her as a sunny but slightly uptight career woman who fought off men's advances.

"My public image is unshakably that of America's wholesome virgin, the girl next door, carefree and brimming with happiness. An image, I can assure you, more make-believe than any film part I ever played," Day told A.E. Hotchner in her memoir, "Doris Day: Her Own Story."

Or as one-time co-star Oscar Levant famously joked, "I knew Doris Day before she was a virgin."

The chaste screen persona seemed at odds with her private life.

She married four times and had a child before she was 20. She described her first husband as a "psychopathic sadist" who beat her. Her second husband told her by letter that he was leaving her after eight months. Husband No. 3 was agent Martin Melcher, who mismanaged her fortune and left her in debt when he died. Her fourth, restaurateur Barry Comden, complained to the press that she kicked him out of bed for her pets.

Day also suffered from panic attacks in the early '50s, what she later described as "tantamount to a nervous breakdown."

As singer, one of 'the best in the business'

She was born Doris Mary Ann von Kappelhoff on April 3, 1922, in Cincinnati.

She dreamed of a career as a dancer until she injured her right leg in a car accident as a teenager. During a long convalescence, she immersed herself in the big-band sounds of Tommy Dorsey and the vocals of Ella Fitzgerald.

She soon became a performer on local radio and then joined a swing band. The bandleader feared that her last name, Kappelhoff ("von" had been dropped), was too long for a marquee, so he dubbed her Doris Day after a song of hers, "Day After Day."

"But I never did like it. Still don't. I think it's a phony name," Day said more than 30 years later.

Photos: Doris Day: Her life in pictures Photos: Doris Day: Her life in pictures Actress Doris Day, one of the biggest box-office stars in Hollywood history, died Monday, May 13, at the age of 97. Hide Caption 1 of 23 Photos: Doris Day: Her life in pictures Doris Day was born in Cincinnati on April 3, 1922. Her birth name was Doris Mary Ann von Kappelhoff. Her parents were William and Alma. William was a music teacher. Hide Caption 2 of 23 Photos: Doris Day: Her life in pictures Day at the age of 4. Hide Caption 3 of 23 Photos: Doris Day: Her life in pictures Day, who gained reputation as a dancer at an early age, poses for a 1937 photo with dancing partner Jerry Doherty. In October of that year, Day seriously injured her right leg in a car accident and decided to concentrate on her singing career. Hide Caption 4 of 23 Photos: Doris Day: Her life in pictures Day became a performer on local radio and then joined a swing band. The bandleader feared that her last name was too long for a marquee, so he dubbed her Doris Day after a song of hers, "Day After Day." In 1947, she signed a contract with Columbia Records. Hide Caption 5 of 23 Photos: Doris Day: Her life in pictures Day made her film debut in 1948's "Romance on the High Seas." Hide Caption 6 of 23 Photos: Doris Day: Her life in pictures Day dances with Gene Nelson on the set of the 1950 film "Tea for Two." Hide Caption 7 of 23 Photos: Doris Day: Her life in pictures Day performs in a scene from 1951's "Lullaby of Broadway." Hide Caption 8 of 23 Photos: Doris Day: Her life in pictures Day with her third husband and manager, Martin Melcher, outside his talent agency in Hollywood. Melcher died unexpectedly in 1968, leaving Day in financial straits. Hide Caption 9 of 23 Photos: Doris Day: Her life in pictures Ronald Reagan holds Day in the 1952 film "The Winning Team." Reagan and Day briefly dated before she married Melcher in 1951. Hide Caption 10 of 23 Photos: Doris Day: Her life in pictures Day sits on a fence with her son, Terry, in front of their home. Terry was her only child. Hide Caption 11 of 23 Photos: Doris Day: Her life in pictures From left, Day, Jimmy Stewart and Richard Wattis star in the 1956 film "The Man Who Knew Too Much." In that movie, Day sang "Que Sera, Sera (Whatever Will Be, Will Be)." The song reached No. 2 on the American Billboard Hot 100 chart, and it sold millions of copies. It also won an Oscar for songwriters Jay Livingston and Ray Evans. Hide Caption 12 of 23 Photos: Doris Day: Her life in pictures From left, Buddy Adler, Day and Tony Curtis pose after the 1958 Golden Globes. Hide Caption 13 of 23 Photos: Doris Day: Her life in pictures Day and Rock Hudson in a scene from the 1959 film "Pillow Talk." Hide Caption 14 of 23 Photos: Doris Day: Her life in pictures Day signs her name in wet cement next to her handprints in Hollywood. In 1960, Day received two stars on the Hollywood Walk of Fame: one for music and one for film. Hide Caption 15 of 23 Photos: Doris Day: Her life in pictures Baseball stars Roger Maris, left, and Mickey Mantle talk with Day on the set of "That Touch of Mink" in 1961. Hide Caption 16 of 23 Photos: Doris Day: Her life in pictures Day poses during a scene from the 1962 film "Billy Rose's Jumbo." Hide Caption 17 of 23 Photos: Doris Day: Her life in pictures In 1965, young women from around the world competed in the International Doris-for-a-Day Look Alike contest. Day is third from left here with the top five finishers. Hide Caption 18 of 23 Photos: Doris Day: Her life in pictures Day is dressed in a mermaid suit from the film "The Glass Bottom Boat" in 1966. Hide Caption 19 of 23 Photos: Doris Day: Her life in pictures Day reads a bedtime story during a scene from "The Doris Day Show" in 1969. Day starred in the TV sitcom from 1968-1973. Hide Caption 20 of 23 Photos: Doris Day: Her life in pictures In 1976, Day released her autobiography "Doris Day: Her Own Story." Hide Caption 21 of 23 Photos: Doris Day: Her life in pictures Day and her fourth husband, Barry Comden pose for a photo. The couple married in 1976 and divorced in 1981. Comden was her last husband. Hide Caption 22 of 23 Photos: Doris Day: Her life in pictures Day and Clint Eastwood attend the Golden Globes in 1989. Hide Caption 23 of 23

Her blonde good looks and smooth, velvety voice ensured that she quickly moved up the musical ranks. As a singer in Les Brown's band, she scored a hit with "Sentimental Journey," a defining ballad for servicemen returning from World War II.

Brown said later, "I'd say that next to Sinatra, Doris is the best in the business on selling a lyric."

Day would record more than 600 songs and nearly 30 albums, including such hits as "It's Magic," "Secret Love," "Que Sera, Sera" and "Everybody Loves a Lover" and concept albums such as 1956's "Day by Day" and 1957's "Day by Night." As recently as 2011, her album "My Heart" made the UK Top 10. She received a Grammy Lifetime Achievement Award in 2008.

Rising star, falling into formula

Her singing popularity led to a movie debut in 1948 in "Romance on the High Seas" and a contract at Warner Bros. Her early peak came in the 1953 Western musical "Calamity Jane."

After her contract ended, she entered the most fruitful period of her career, including dramatic parts in "Love Me or Leave Me," opposite James Cagney, and in Alfred Hitchcock's "The Man Who Knew Too Much," starring James Stewart.

Day played a dramatic role with James Stewart in Alfred Hitchcock's "The Man Who Knew Too Much."

Day turned almost exclusively to comedies by the late '50s. "Pillow Talk" and "Lover Come Back" opposite Rock Hudson and "That Touch of Mink" with Cary Grant cemented her goody-two-shoes reputation, if sometimes unfairly: The films were about Day, usually cast as an independent working woman, resisting her leading man's charms because she'd been deceived more than to protect her virginity.

Though the increasingly formulaic films were successful, they'd prove to be Day's undoing and make her passé when the counterculture supplanted the "Mad Men" era.

In a review of her last film, 1968's "With Six You Get Eggroll," Vincent Canby summed up the critical attitude toward Day then, noting that there were "some hints of the very real comic talent that has, over the years, become hermetically sealed inside a lacquered personality, like a butterfly in a Mason jar."

She had a chance to change course when director Mike Nichols offered her the role of Mrs. Robinson in "The Graduate," but the star wasn't interested. "I could not see myself rolling around in the sheets with a young man half my age whom I'd seduced," she recalled later. "I realized it was an effective part ... but it offended my sense of values."

With his wife's film career in decline due to mediocre movies he initiated, husband Melcher began to explore options on TV despite her opposition. A perfectionist, Day feared the medium's quick production pace.

Melcher died unexpectedly in 1968, leaving Day with a CBS sitcom and in financial straits. Her husband's reliance on attorney Jerome Rosenthal for business advice proved disastrous: The lawyer went through Day's millions with bad investments in oil wells, cattle and hotels.

Day, with husband and manager Marty Melcher, outside his talent agency in Hollywood, circa 1960.

"I don't know if Marty betrayed me or not. I tend to think he didn't betray me. I think he loved me," she told the Los Angeles Times two decades later about her husband's management.

"The Doris Day Show" proved to be a lifesaver. Despite an ever-changing format, it ran for five seasons, gave her financial stability and kept her working as she coped with the loss of her spouse of 17 years. Day sued Rosenthal for mismanagement and won a $20 million-plus verdict in 1974 after years of litigation (she later settled with insurers).

Activist for animals

By the mid-'70s, she withdrew from the limelight to focus on animal rights and set up the Doris Day Animal League and Doris Day Animal Foundation. In a 2012 interview with "Fresh Air" host Terry Gross, Day admitted that she had about 30 dogs at one point.

"All my life, I have never felt lonely with a dog I loved at my side, no matter how many times I've been alone," she said in her memoir.

As a staunch advocate for animals, she briefly came out of retirement to host a cable TV pet show called "Doris Day's Best Friends," which included an emotional reunion with three-time co-star Hudson shortly before his death in 1985.

Perhaps her closest friend, son Terry Melcher, a music producer, died in 2004 at 62. He was survived by his son, Ryan.

There was talk of comebacks: She reportedly was offered "Murder, She Wrote" and the Debbie Reynolds role in "Mother" in 1996. But she resisted Hollywood overtures. In 2015, she batted down reports she was to appear in a Clint Eastwood film.

During her career and retirement, Day always seemed to adhere to the philosophy of her biggest hit, "Que Sera, Sera," which she initially opposed as a "kiddie song" but which became her signature tune.

"Que sera, sera.

Whatever will be, will be;

The future's not ours to see.

Que sera, sera,

What will be, will be."

Reaction to her death poured in from Hollywood.

Condolences to the family of Doris Day. She was the World's Sweetheart and beloved by all. ❤️ Que Será, Será!😞 — William Shatner (@WilliamShatner) May 13, 2019

We've lost another great Hollywood talent. Take a minute to appreciate the legendary Doris Day: https://t.co/72ssvivryz — Seth MacFarlane (@SethMacFarlane) May 13, 2019

Once I had a secret love

That lived within the heart of me

All too soon my secret love

Became impatient to be free



I will miss you Doris Day , my first secret love — Paulo Coelho (@paulocoelho) May 13, 2019

"Condolences to the family of Doris Day," actor William Shatner tweeted. "She was the World's Sweetheart and beloved by all. Que Será, Será!"