Dr. Oz recently learned that his mother, Suna Oz, has Alzheimer’s disease.

“I’m feeling guilty because I completely missed the signs until fairly late in the process,” he told People magazine, saying it was a “gut punch.”

Dr. Oz, whose father died last February, also revealed that he and his two sisters noticed different irregularities in their mom’s actions.

For example, he saw that she was struggling to find her words, while his sister thought she was dressing oddly. But the siblings did not put the signs together.

“If the right word was, ‘You look beautiful today,’ she would use, ‘You look pretty prettier today.’ I missed those clues,” he told the outlet. “Alzheimer’s is like a snake in the grass. You don’t see it. You only see the effects of it suddenly. And if there’s a wind blowing the grass, you don’t even notice the grass moving strangely. It sneaks up on you.”

Read more at People.