Simplify the following text for a Grade 2 native English-speaking person.
Original: Louis died of a heart attack in Desert Springs Hospital on April 12 , 1981 , just hours after his last public appearance viewing the Larry Holmes-Trevor Berbick heavyweight championship . Ronald Reagan waived the eligibility rules for burial at Arlington National Cemetery , and Louis was buried there with full military honors on April 21 , 1981 .
Simplified: Louis died on April 12 , 1981 .