'All That' Star Christy Knowings Cause of Death Revealed

Christy Knowings' cause of death has been revealed ... the former "All That" star died after suffering cardiac arrest ... TMZ has learned.

According to a death certificate obtained by PEOPLE, the certificate identifies asthma as the underlying cause, with status asthmaticus and acute hypoxic respiratory failure listed as contributing conditions.

We broke the story ... Knowings was hospitalized in August after suffering an asthma attack that caused brain damage. A family member told us she was placed on life support, and her loved ones ultimately made the difficult decision to take her off it several days later.

Knowings joined Nickelodeon's "All That" in 1997 after appearing in "And Now This," a Rosie O’Donnell sketch comedy special produced by the network.

She spent three seasons on "All That," playing several characters, including Penny Lane and Jessica in the recurring "Whateverrr!!!" sketch alongside Amanda Bynes.

Christy later appeared in three episodes of "Sesame Street" with her real-life twin brother, Chris Knowings. Christy was the second former "All That" cast member to die this year. As TMZ previously reported, Kianna Underwood was killed in a hit-and-run collision in Brooklyn in January.