Credit: Fred Duval/FilmMagic

Amy Winehouse was drug-free when she passed away at age 27 in London on July 23.

A rep for the late "Rehab" singer's family confirmed the results of a toxicology test in a statement last month. But the singer's father, Mitch, thinks she suffered a fatal seizure related to alcohol detoxification.

"Everything Amy did, she did to excess," Mitch told Anderson Cooper, as excerpted by the Associated Press. "She drank to excess and did detox to excess."

Mitch said the "Valerie" songstress had suffered seizures where she would lose consciousness. "[But] when she wasn't drinking," her father said, "she was absolutely on top of the world."

The Winehouse family released a statement last month acknowledging that Amy's autopsy report showed there was alcohol present. "But it cannot be determined as yet if it played a role in her death," they added. A definitive cause of death is expected to be determined in October.

In July, Mitch told Us Weekly: "Three years ago, Amy conquered her drug dependency. The doctors said it was impossible, but she really did it. She was trying hard to deal with her drinking."

Watch the full interview with Mitch Winehouse this Monday on Anderson. Check your local listings for tune-in times.