"A day of saying hasta luego to two great ladies, Nora Ephron and Doris Singleton," Arnaz wrote on her Facebook page. "May they both fly swiftly heavenward and enjoy a blissful rest for jobs well done down here. They were loved and appreciated and will be missed."
Singleton was 92 and died Tuesday in Los Angeles, reports Variety.
Playing the competitive neighbor Appleby, who liked to boast about her son Stevie (which forced Lucy to brag about Little Ricky), Singleton first met Ball in the late 1940s, while the redhead was on radio doing My Favorite Husband, which evolved into I Love Lucy.
In a 2005 interview with the Archive of American Television, Singleton recalled her first TV episode, among other memories, and how Carolyn was actually the name of Lucille Ball's schoolteacher.
Of Ball, Singleton said, "She was nice to me, and she really liked my work." If she didn't like you, the actress noted, "You didn't come back."
Singleton appeared on Lucy 10 times between 1953 and 1957, and also appeared on Ball's later TV shows. She gave another memorable performance as the sequestered hotel roommate of Edith Bunker (Jean Stapleton) on the 1971 All in the Family episode, "Edith Has Jury Duty."
In addition, she appeared on such shows as Adventures of Superman, Hogan's Heroes, My Three Sons, Hazel, The Munsters, The Dick Van Dyke Show, Gomer Pyle, U.S.M.C., The Fugitive, The F.B.I., Marcus Welby, M.D., Phyllis, Days of Our Lives and Dynasty, the Hollywood Reporter lists.
Entering showbiz as a teenager, the Brooklyn-born Singleton danced with the American Ballet Theater and sang with bandleader Art Jarrett. With her smooth, distinctive voice, she later acted on radio, appearing with George Burns and Gracie Allen, Bob Hope and Jack Benny in radio.
Singleton's husband of 61 years, comedy writer, director and producer Charles Isaacs, died in 2002.