People who have Capgras believed the people closest to them are replicas, clever fakes that look like their loved ones but are not.
My old boss’s dad suffered from Capgras, probably as part of his Alzheimers. I remember once she said she visited him and he asked who she was. “I’m Jan, Dad,” she said.
He gave her a patronizing smile. “Oh, you’re not Jan.” He looked at her closely. “They didn’t even do a good job when they made you.” He seemed to think she was some kind of alien.
While my dad had Alzheimers, he always seemed to know who I was, even when he didn't know my name.
Read and hear more about Capgras here.