Actress Erin Moran likely died due to complications of stage four cancer, the Harrison County Sheriff's Department and the Harrison County Coroner's Office said in a joint statement on Monday.
The Happy Days star was found deceased upon arrival on Saturday after police received a 911 call in reference to an unresponsive female, a police spokesperson previously told ET. She was 56 years old.
"On Saturday, the 22nd day of April, 2017, Erin Marie Moran-Fleischmann passed away at her residence located in New Salisbury, Indiana," the joint statement reads. "A subsequent autopsy revealed that Mrs. Moran likely succumbed to complications of stage 4 cancer. Standard toxicology tests were performed and the results are pending, however, no illegal narcotics were found at the residence."
WATCH: 'Happy Days' Star Erin Moran Dies at 56
Moran was best known for her role as Joanie Cunningham on Happy Days. She later went on to star in her own spinoff, Joanie Loves Chachi, based on her character's relationship with Chachi Arcola (Scott Baio).
A number of Moran's Happy Days co-stars have expressed their sadness at Moran's death, including actress Marion Ross, who played her mother on the beloved show.
"I am just devastated to hear about Erin's passing," Ross told ET on Saturday. "She was so cute and bright and great on the set of our show. We would send her off to school and she would come back to the set and pick right up on what she had to do! She was so adaptable, so talented. She got cuter and cuter every year! In 2007, dear Florence Henderson and her daughter, Susan, Erin and I christened the Love Boat cruise ship in Athens, Greece. Again, I am devastated, but I will always remember Erin."
"Such sad sad news," Ron Howard -- who played her older brother, Richie -- tweeted. "RIP Erin. I'll always choose to remember you on our show making scenes better, getting laughs and lighting up tv screens."
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Last July, Howard got emotional when he talked to ET about the loss of his mentor, the late Garry Marshall, who created Happy Days.