Beloved stage and TV actress Katherine Helmond, best known for her work on "Who's the Boss?" and "Soap," has died, her agent told NBC News.

She was 89.

Helmond, who had been suffering from Alzheimer's disease, passed away on Saturday in Los Angeles, according to Variety.

"My beautiful, kind, funny, gracious, compassionate, rock," Helmond's "Who's the Boss" granddaughter Alyssa Milano tweeted in tribute.

"You were an instrumental part of my life. You taught me to hold my head above the marsh! You taught me to do anything for a laugh! What an example you were!" Milano said.

TV viewers got to know Helmond as the ditzy but lovable Mona Tate, on the 1970s show "Soap," which ran from fall, 1977 until 1981.

A whole new generation of fans watched her perform on "Who's the Boss?" as the outgoing but often outrageous mother of star Tony Danza's employer. That show ran from fall 1984 to spring of 1992.

Helmond was often cast to play older, sexually-liberated characters.

“I thought Mona was terrific,” Helmond once told People magazine about her "Boss" character. “She wasn’t a slut, but suddenly in her life she had the freedom to flirt and date. I hope I projected a positive image to older women."

Before TV, Helmond enjoyed a successful stage career. She was nominated for a 1973 Tony Award for best actress for her role in "The Great God Brown."