One week after publicly revealing his struggle with the brain disease, he will appear on Dr. Phil Wednesday to discuss how it's affected his life. The Partridge Family actor says he first noticed symptoms of the disease two and half years ago. "When friends of yours or family members begin to tell you and say to you—'Remember? I just told you this two days ago?'—and there's no memory of it, that's when I began to be very concerned," he tells Dr. Phil McGraw. After seeing his own mother "disappear" to the same disease, he told his 26-year-old son, Beau Cassidy, "I want you to promise me you'll find a way to let me go. Don't let me live like that."