Pope John Paul, himself in fragile health, sent a message of support to Monaco's Prince Rainier today but doctors said they were "extremely cautious" about the ailing monarch's chances of survival.
The 81-year-old Rainier, widower of Hollywood film star Grace Kelly, has been suffering from a lung infection complicated by cardiac and kidney problems. He was clinging to life in the intensive care unit of a hospital in the Mediterranean principality his family has ruled for 700 years.
"The health of his Most Serene Highness Prince Rainier III is continuing to worsen," the palace said in a medical bulletin.
"Despite the most appropriate treatment, and having controlled his bronchial-lung infection, the functioning of his heart, lungs and kidneys is progressively deteriorating."
The bulletin said the doctors were "extremely cautious" about Rainier's "prospects for survival".
The 84-year-old Pontiff sent a missive to the prince on a subdued Easter weekend in the tiny, French Riviera state.
"Informed of the trial of ill-health that has struck his Most Serene Highness, the Holy Father joins him by sending warm wishes through thought and prayer," the Pope said.
Monaco citizens meanwhile were keeping an anxious eye on the white flag flying at full-mast from the prince's palace, built on the coastal rock Rainier's ancestor Francois Grimaldi seized from the Genoese in 1297. Should one of Europe's oldest and longest-serving monarchs pass away, his son Albert, 47, is expected to take his place.