She had devoted much of her time recently advocating for animal rights.
Day's Foundation attributed the death to pneumonia, noting the star had been in excellent health until the recent illness.
Tributes flowed on Monday after the sad news broke.
"Oh Ms. Day, A Cincinnati girl just like me".
"But I wonder if I would, you never know". "I'm often asked, 'Who would you like to interview?'" he said, explaining his regret he never got to interview the star. "Godspeed. RIP", Sarah Jessica Parker said via Instagram.
Bashara said Day's estate will be donated to charity as per her will. "She was surrounded by a few loved ones".
"She was guileless, and I had discussions with her about how popular she was, and she would say, "I don't understand it" about why she was so loved".
Beyond her life on the big screen, Day released 29 studio albums of music between 1949 and 2011.More news: ‘Empire’ will end with Season 6
It was only when a vehicle accident left her with two broken legs that the 13-year-old turned to singing. "We will miss her handsome smile".
The Humane Society of the United States, of which The Doris Day Animal League is an affiliate, praised Day as a pioneer in animal protection.
Born Doris Mary Kappelhoff on April 3, 1922, Day's goal as a child was to be a dancer but a serious vehicle accident when she was very young cut those dreams short. She abandoned that dream after her right leg was broken in an auto accident.
Day sang "Que Sera, Sera" for the film, which later became the theme song to The Doris Day Show, according to Biography. "She could sing light or strong in any part of her range". Playing Jo McKenna, one-half of an American couple whose vacation turns tragic after their child, Hank, is taken, she and her husband (Stewart) must follow various clues to find him, ultimately realizing he's being held at an embassy.
Day was cast in "Romance on the High Seas" after Judy Garland and Betty Hutton bowed out.
"When I met Ruth I thought I was getting Doris Day!" he tweeted, sharing pictures of his famous wife and the late icon side-by-side. The pair would team up again in 1961's Lover Come Back and 1964's Send Me No Flowers.
When her third husband, film producer Martin Melcher, died in 1968, Day was shocked to learn that he and his business partner, Jerome Bernard Rosenthal, had squandered her earnings for 17 years.
She added: "I think the reason people liked our movies is because they could tell how much we liked each other".
She also went on to star in "The Doris Day Show", a sitcom that lasted for five seasons (1968-1973). "The story I have heard the most is that at one point Doris was up for a role when quite young and her age may have been miswritten on the audition form".
Day married a fourth time at age 52, to Barry Comden, who was a maitre d' in Beverly Hills, in 1976.