Erin Moran, best known for playing Joanie Cunningham on Happy days, has died aged 56.
According to TMZ, the actress was found unresponsive on Saturday afternoon by authorities in Indiana.
The cause of death is unknown.
Police told E! News in a statement: "On April 22, 2017 at approximately 4:07 p.m., the Harrison County Sheriffs Department received a 911 call that referenced an unresponsive female.
"Upon the arrival of first responders, it was determined that Erin Marie Moran Fleischmann was deceased and an autopsy is pending."
Henry Winkler, who starred opposite Moran as The Fonz in the iconic series, tweeted: "OH Erin...now you will finally have the peace you wanted so badly here on earth. Rest In It serenely now...too soon."
While Ron Howard shared: "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."
"What happened with all of us was like we were this family," Moran said in a 2009 interview with Xfinity.
"It was so surreal with all the cast members...They were my family, get it?"
"I liked working with the people. But I didn't even want to do it. I was talked into it," she said. "I wanted to stay on 'Happy Days.' They were running them at the same time."
The California-born actress, who also starred in Happy Days spinoff Joanie Loves Chachi, had fallen on hard times in recent years.
She was reportedly kicked out of her trailer park in Indiana, along with her husband, because of their hard-partying ways.
Erin was just 14 when she signed on to play Ron Howard's sister in the TV classic Happy Days, which aired from 1974 to 1983.
Her TV credits also include The Love Boat, Murder, She Wrote and The Bold and the Beautiful.
She most recently appeared on VH1 reality show Celebrity Fit Club in 2008 and low-budget film Not Another B Movie 2010.