"Juan" makes his will. A year later, he is diagnosed with Alzheimer's disease, and so loses testamentary capacity. Often, the medical diagnosis for Alzheimer's comes well after the victim's judgement becomes impaired.
Based on his later diagnosis, would a court be likely to say that Juan lacked testamentary capacity at the time of the writing?
Note: while tagged united-states and texas, I am also interested in how this would be interpreted elsewhere.