Jack Hanna, the former director of Ohio's Columbus Zoo and Aquarium, has been diagnosed with dementia, his family announced Wednesday.
The wildlife expert's family shared a letter on his official Twitter account detailing that his condition, which they said is "now believed to be Alzheimer's," has "progressed much faster in the last few months" than they expected.
They explained that because of this, Hanna, who announced his retirement from the Columbus Zoo in June 2020, is stepping back from public life.
"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," the letter read.
MORE: Columbus Zoo’s Jack Hanna retires after 42 years"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," the note continued. "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."
"He’s always said, 'You have to touch the heart to teach the mind,'" they wrote. "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."
Hanna's daughters, Kathaleen, Julie and Suzanne, also highlighted his "impactful" contributions to wildlife conversation efforts through his media appearances and advocacy efforts.
They said they are "abundantly proud to be his daughters."
In their note, the trio also praised their mother, Suzi, who Hanna married in 1968.
"Our mom -- Suzi -- has been by his side for 53 years in every corner of the world," they wrote. "She continues to be his rock (and ours, too)."
"We have great respect and admiration for Mom as we move through not only this difficult time with Dad, but also Julie’s continued life-long challenges from her childhood leukemia, as she is currently recovering from major surgery," they added.
Despite his condition, Hanna's daughters said his "great sense of humor continues to shine through" and confirmed that "yes -- he still wears his khakis at home."
The Hanna family asked for privacy during this time.