Complex sentence: On 1 April 2005, the Palace announced that Rainier's doctors believe his chances of recovery were "slim"; on 6 April it announced that Prince Rainier had died in Cardiothoracic Center of Monaco in Monaco at 6:35 AM local time at the age of 81.
Split into simpler sentences: On 1 April 2005, the Palace announced that Rainier's doctors believe his chances of recovery were "slim". On 6 April, Prince Rainier died at the Cardiothoracic Center of Monaco at 6:35 AM local time at the age of 81.