“Most people think your husband killed himself because he was depressed,” says Amy Robach in an ABC News interview with Robin Williams’ widow Susan Miller, the first since his death in August, 2014.

“No!” said Miller. The disease that led to Robin Williams’ suicide wasn’t depression, she said. “Lewy body dementia killed Robin. It’s what took his life.”

The disease, the second most common form of dementia after Alzheimer’s, shows itself in many unpredictable ways and so often eludes a proper diagnosis. To learn more, see Parkinson’s, Alzheimer’s or Lewy Body Dementia—Don’t Be Misdiagnosed Like Robin Williams Was.