In an interview with "20/20", Ron Reagan, the son of President Ronald Reagan, said that when his father was in office, no one thought he had Alzheimer's disease -- the devastating illness he was diagnosed with less than two years after leaving the White House.
But Ron Reagan said that he did notice something had changed about his father during his presidency.The father and son often had spirited, fast-paced political debates when Ron visited the president at the White House. But during one such debate, Ron Reagan grew concerned.
"There was just something that was off. I couldn't quite put my finger on it," he told "20/20's" Elizabeth Vargas.
Watch Elizabeth Vargas' interview with Ron Reagan on "20/20" TONIGHT at 10 p.m. ET.
Ron Reagan grew worried enough to spend a day at the White House shadowing the president. That was when he noticed something else -- his father was reading note cards as he made phone calls. It wasn't an obvious sign that something was wrong, but it bothered Ron Reagan nonetheless.
"It wasn't like oh my God he doesn't remember he's President...You know, it was just -- I had an inkling something was going on," he said.
In hindsight, Ron Reagan believes what he say were early signs of Alzheimer's. But Reagan is adamant that his father's illness shouldn't mar his legacy.
"This no more discredits or defines his presidency than Lincoln's chronic depression, Roosevelt's polio, Kennedy's Addison Disease any of those things," he said. "You can't define their presidencies in terms of that."
To mark the hundredth anniversary of President Ronald Reagan's birth, son Ron Reagan has written "My Father at 100: A Memoir." Read an excerpt of the book below, CLICK HERE for photos of Ronald and Ron Reagan.
We all cobble together an internal account of our lives; in that, Dad was entirely typical. Virtually everyone creates a mental album of memories and anecdotes that, ultimately, passes for our version of a life story. We are all the protagonists of our own narratives, of course -- the indispensable main character; on a good day, the hero. In that sense, Dad was just like everyone else. Only peculiarly more so. For most of us, the boundaries of our personal tale are relatively fluid and amenable to outside influence. Our story selection, even the sense of our own character, shifts as new circumstances arise: One day we're a rebel folk hero in the making, the next day, a contented corporate cog. But Dad's story, I believe, was far more comprehensive in its sweep and consistent in its narrative details than is the case for most people. Keeping its primary themes intact and inviolate, safe from the depredations of an intrusive, ambiguous, and contradictory world, was for him an endeavor of existential import. My father didn't create his personal narrative to put one over on anyone. On the contrary, with its creation, he was forming a template for his life. He wanted to be seen -- he wanted to truly be -- an estimable individual who made his way through life as a positive force in the world, a man people would admire for all the right reasons.