Palace officials in Monaco say Prince Rainier's condition remains stable but fragile Tuesday.
In a statement, the officials say the 81-year-old prince remains on a respirator, and his prognosis is, "extremely reserved."
The 81-year-old monarch was hospitalized three weeks ago suffering from heart, lung and kidney problems.
Prince Rainier has occupied the throne of Monaco since 1949, making him one of Europe's longest reigning monarchs. His Grimaldi family has ruled the tiny Mediterranean principality since the 13th century.
Some information for this report provided by AP and AFP.