Jack Hanna has been diagnosed with dementia and will retire from public life, his family says

• Former Columbus Zoo director Jack Hanna, 74, has been diagnosed with dementia.
• His daughters say the famed zookeeper's dementia is believed to be Alzheimer's disease.
• In a letter shared on Twitter, Hanna's daughters said he would be retiring from public life.

Former Columbus Zoo director Jack Hanna has been diagnosed with dementia, his family announced in a letter on Twitter.

In the letter, the famed zookeeper's daughters Kathaleen, Suzanne, and Julie Hanna wrote that their father would be retiring from public life, months after retiring from his role at the Columbus Zoo, where he worked for 42 years.

They said Hanna, 74, is believed to have Alzheimer's disease and that his condition has progressed "much faster in the last few months than any of us could have anticipated."

"A passion for wildlife conservation and education has been at the core of who our dad is and everything he has accomplished with the help of so many. He has spent his life connecting people and wildlife because he has always believed that having people see and experience animals is key to engaging them in more impactful conservation efforts," his daughters said. "Even though Dad is no longer able to travel and work in the same way, we know that his infectious enthusiasm has touched many hearts and will continue to be his legacy."

Alongside his work at the Columbus Zoo, Hanna regularly made media appearances and took part in a number of nature TV shows, including "Animal Adventures," "Into the Wild," and "Wild Countdown."

Ohio Governor Mike DeWine said on Twitter that he was "very sad" to learn of Hanna's diagnosis.

"Over the years, [my wife] Fran and I have had the opportunity to take our kids and grandkids to the Columbus Zoo and Aquarium and The Wilds," he said. "When we were there with Jack, we were so fortunate to experience his passion for animals and the natural world."