AceShowbiz - David Gail's sudden death is currently under investigation by authorities. As the cause of death remains unknown pending toxicology tests, cops are looking into the possibility of a fatal drug overdose, according to a new report.

Law enforcement sources told TMZ on Monday, January 22 that no foul play is suspected in the actor's case, but police are awaiting for toxicology tests to determine an official cause of death. Police suspected that the "Beverly Hills, 90210" alum may have overdosed, but it is unknown what types of substances they are considering in the case.

David's sister Katie Colmenares confirmed his death via Instagram on Saturday, January 20. Katie wrote along with a picture of the two embracing on the front porch, "There's barely been even a day in my life when you were not with me by my side always my wingman always my best friend ready to face anything and anyone w me the bears will never be the same."

"But I will hold you so tight every day in my heart you gorgeous loving amazing fierce human being," she added. "Missing you every second of every day forever there will never be another."

Katie did not give her brother's cause of death. He was 58.

Following the shocking news, fans have sent their condolences via social media. "Beautiful words about David. Sorry for your loss. You had a great brother," one person wrote. "He was always full of fun, laughs & love. Will cherish my friendship with him. Sending Love to your family!" another added.

David was best known for playing Stuart Carson, the fiance to Brenda Walsh (Shannen Doherty) on "Beverly Hills, 90210". He also starred as Dr. Joe Scanlon on ABC's soap opera "Port Charles", a spin-off to "General Hospital", from 1999 to 2000.

Shannen paid tribute to her former co-star on Monday by sharing on her Instagram Story a captionless photo of the pair dancing.