Pat Summitt.

Robin Williams.

And now David Cassidy.

The list of celebrities with early-onset dementia continues to grow.

Cassidy, 66, spoke about his 2014 diagnosis at length on the “Dr. Phil” show this month.

“When friends of yours or family members begin to 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.”

The singer — who has publicly battled alcohol and substance abuse issues — said he went public with his condition because, after a recent performance in which he looked and sounded unsteady and ultimately fell off the stage, he didn’t want fans to think he’d relapsed. He had planned to stop performing after 2017 — but will likely curtail his touring immediately.

Cassidy is cognizant that he’s declining, but he’s still lucid and able to function.

Both Cassidy’s mother and grandfather succumbed to dementia, so the former “Partridge Family” star has no illusions about what awaits him.

He recounted on “Dr. Phil” that, after watching his mother’s heart-wrenching decline, he didn’t want his son Beau to have a similar experience, so he said to the 26-year-old, “I want you to promise me you’ll find a way to let me go. Don’t let me live like that.”

He told People magazine that for now he wants to stay focused and “enjoy life.”

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