Erin Moran's 'Happy Days' Co-Stars Mourn Her Death: 'Such Sad Sad News'

She was found unresponsive in her home on Saturday afternoon.

Erin Moran’s former co-stars on the classic sitcom Happy Days are in mourning following the death of the star at 56.

Moran, who played Joanie Cunningham in the series, died Saturday. She was found unresponsive in her home after a 911 call was placed, according to authorities.

Read: Erin Moran Went from 'Happy Days' to Hard Times

The cause of her death was reportedly undetermined, but an autopsy is pending.

Moran joined the Happy Days cast at the age of 13 as the kid sister of Richie Cunningham (Ron Howard).

The popular show, set in the 1950s, ended in 1984 after a 10-year run.

Moran revived her role in the spinoff Joanie Loves Chachi with actor Scott Baio from 1982 to 1984.

Howard tweeted Saturday night about the loss.

Happy Days co-star Henry Winkler, who played Arthur “Fonzie" Fonzarelli, also paid tribute to the late star via Twitter.

“Now you will finally have the peace you wanted so badly here on earth," Winkler wrote. “Rest In It serenely now.. too soon."

Read: Scott Baio Is Done Helping Erin Moran

In 2012, Moran was living in a trailer park in Indiana, the same year she won $65,000 in a settlement with CBS over merchandising payments from Happy Days.

She sued the network alongside actors Anson Williams, Don Most and Marion Ross, claiming they lost out on millions in royalties after their photos were used on DVDs, according to the New York Daily News

In 2010, Moran lived in Palmdale, Calif., but lost her home to foreclosure.

Watch: Carrie Fisher, 'Star Wars' Actress and Author, Dies at 60