Erin Moran, best known to TV audiences for her role as Joanie Cunningham on the classic sitcom Happy Days, has died, TMZ reports. She was 56.

Moran rose to fame when she was cast as the younger sister of Ron Howard’s Richie Cunningham on Happy Days, which ran for 11 seasons between 1974 and 1984. She later co-starred opposite Scott Baio in the short-lived spinoff Joanie Loves Chachi, which lasted for just two brief seasons between 1982 and 1983.

Additional TV credits include episodes of Family Affair, The Love Boat, Murder, She Wrote, Diagnosis Murder and The Bold and the Beautiful. In 2008, she appeared on VH1’s Celebrity Fit Club.

A cause of death has not been revealed. UPDATE: Per a preliminary autopsy report, Moran died of Stage 4 cancer.

Such sad sad news. RIP Erin. I'll always choose to remember you on our show making scenes better, getting laughs and lighting up tv screens. https://t.co/8HmdL0JKlf — Ron Howard (@RealRonHoward) April 23, 2017

OH Erin… now you will finally have the peace you wanted so badly here on earth …Rest In It serenely now.. too soon — Henry Winkler (@hwinkler4real) April 23, 2017