She was one of the biggest box office stars in Hollywood in her day — and one of the most popular entertainers in the United States.

Now, the multi-talented Doris Day has died at the age of 97.

The Doris Day Animal Foundation confirmed that she died early on Monday at her home in Carmel Valley, California.

In an emailed statement, the foundation said she was surrounded by close friends and that she “had been in excellent physical health for her age, until recently contracting a serious case of pneumonia,” as many media outlets reported.

The singer and actress of film dramas and musicals was a top star in the 1950s and 1960s.

Related: Slideshow: 10 Golden Age Movie Stars Who Are Still with Us

Day was associated with many recordings — yet her most famous and signature song was “Que Sera, Sera” (“Whatever Will Be, Will Be”), from Alfred Hitchcock’s 1956 film “The Man Who Knew Too Much.”

She also went on to star in “The Doris Day Show,” a sitcom that lasted for five seasons (1968-1973).

After she walked away from acting, Day turned her focus to animal welfare with the Doris Day Animal Foundation.

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“May she rest in peace,” many Americans tweeted as soon as the news broke.

See more in the tweets below.