Cindy Williams, who played the cheerful but demure Shirley Feeney in the popular TV sitcom “Happy Days” and its spinoff “Laverne & Shirley,” has died. She was 75.

Williams’ children, Zak and Emily Hudson, told the Associated Press through family spokesperson Liza Cranis that Williams died in Los Angeles on Jan. 25 after a brief illness. The news was also posted on Williams’ official website.

“The passing of our kind, hilarious mother, Cindy Williams, has brought us insurmountable sadness that could never truly be expressed,” the statement said. “Knowing and loving her has been our joy and privilege. She was one of a kind, beautiful, generous and possessed a brilliant sense of humor and a glittering spirit that everyone loved.”

Williams scored her big break in 1975, when she and Penny Marshall were cast in ABC’s “Happy Days” as Shirley and her best friend Laverne DeFazio, who went on a double date with Richie (Ron Howard) and Fonzie (Henry Winkler). The guest appearance was so popular that it led to their own spinoff, “Laverne & Shirley,” which followed the friends’ lives as roommates and co-workers at Shotz Brewery. The show ran for eight seasons from 1976 to 1983, becoming the most-watched show on television by its third season and garnering six Golden Globes nominations and one Emmy nomination. Williams departed the show in its eighth and final season after she became pregnant with her first child.

“Cindy has been my friend and professional colleague since I met her on the set of “Happy Days” in 1975. Not once have I ever been in her presence when she wasn’t gracious, thoughtful and kind,” Winkler said in a statement after Williams’ death. “Cindy’s talent was limitless. There was not a genre she could not conquer. I am so glad I knew her.”

Born in Van Nuys, Calif. on Aug. 22, 1947, Williams’ love for acting began at Birmingham High School. She attended Los Angeles City College as a theater major. After scoring several commercial spots, Williams transitioned to television in the early ’70s with small roles on shows like “Room 222,” “Barefoot in the Park,” “Nanny and the Professor” and “Love, American Style.” But Williams truly broke out in George Lucas’ 1973 coming-of-age film “American Graffiti” as Laurie Henderson, which earned her a BAFTA nomination for best actress in a supporting role. Williams also scored a role in Francis Ford Coppola’s “The Conversation” in 1974, starring alongside Gene Hackman, Harrison Ford and Robert Duvall.

After the success of “Laverne & Shirley,” Williams returned to sitcoms in the ’90s, starring in “Normal Life” and “Getting By,” which was made by “Laverne & Shirley” producers Thomas L. Miller and Robert L. Boyett. Williams’ other film and TV credits include “Bingo,” “Meet Wally Sparks,” “The Biggest Fan,” “Strip Mall,” “For Your Love,” “7th Heaven,” “8 Simple Rules” and “Girlfriends.” In 2013, Williams and Marshall reunited for an episode of Nickelodeon’s “Sam & Cat,” in which they play the creators of a ’70s sitcom.

According to producer and friend Bruce Kimmel, Williams had been working on a new show that is set to premiere this year. “Cindy was really looking forward to promoting her new project, the short form musical series, “Sami,” which will premiere in April on Amazon Prime,” Kimmel said in a statement to Variety. “I’ve known her since we began LACC in 1965, have loved her from the moment I laid eyes on her and have had so many incredible adventures with her. We were as close as close can be, from then until now. And I’ve been watching her constantly as we’ve been editing the web series we just did and wrapped only two months ago. I’m so grateful to have had her be such an important part of my life for close to 60 years. I will miss her like crazy, but I’m just so happy we got to work together one final time and I can’t wait for the show to air — she was funny, charming and brilliant right up to the end. I’ve never known anyone like her.”

Williams was married to Bill Hudson of the Hudson Brothers from 1982 to 2000, when they divorced. She is survived by her two children, Zak and Emily.