It's brother vs. brother as Ronald Reagan's sons slug it out in a nasty public feud.
Michael also launched a Twitter attack on his brother, who famously raised eyebrows when he dropped out of Yale to become a ballet dancer in 1976.
"Ron, my brother, was an embarrassment to his father when he was alive and today he became an embarrassment to his mother," Michael wrote.
Michael reportedly has not spoken to Ron since shortly after their father's funeral.
The latest controversy has been sparked by Ron's new book, in which he makes the explosive claim that his father showed signs of Alzheimer's as early as his first term in the White House.
Reagan died from Alzheimer's in 2004. But he was not officially diagnosed till five years after he left office.
"I had an inkling there might be something going on. Knowing what we know now about the nature of Alzheimer's disease, we know that decades ahead of symptoms arriving. Changes are happening in the brain," said Ron Reagan Jr. on 20/20.
Ron also said that if his dad had been diagnosed with Alzheimer's while he was President, he would have stepped down.