I remember a couple years ago when Kid and I were at summer camp, I got a raging text from ex demanding to know where Kid was because I was supposed to bring her to his apartment for a visit. I responded that we were at the camp, that she had been at his apartment for a visit yesterday, just before we left town for camp, and provided a screenshot of the texts we had exchanged ("on our way now", "okay see you" etc). So not only had he forgotten what day it was, he had also forgotten that he had seen his daughter less than 24 hours previously. And his self-righteous rant at me was right under the texts from the previous day on his phone.
That was when I knew for sure, beyond just wondering, that there was something really cognitively wrong with him.