Jack Hanna has been diagnosed with dementia and will retire from public life, according to a letter shared by his family on Wednesday. He was director of the Columbus Zoo from 1978 to 1992 and still serves as its director emeritus.

In the letter, Jack's daughters Kathaleen, Suzanne and Julie Hanna stated their dad was diagnosed with dementia, now believed to be Alzheimer’s; his condition progressed much faster than expected in the last few months.

"Sadly, Dad is no longer able to participate in public life as he used to, where people all over the world watched, learned and laughed alongside him," his daughters wrote.

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