Doctors are not sure if Prince Rainier III of Monaco recovers from the heart, lung and kidney malfunction that forced him to be rushed to the intensive care unit four days ago.

"The state of health of His Most Serene Highness Prince Rainier III, who is still in intensive care under artificial respiration in Monaco’s Cardiothoracic Centre, remains worrying," was said in a medical bulletin issued Thursday.

Rainier was visited by his three children from the movie-star Grace Kelly whom he married in 1956 and who died in a car crash in 1982. Crown Prince Albert, 47, his heir, came from abroad to visit his father, Princess Caroline, 48, also visited Rainier, Princess Stephanie, 40, was seen entering and leaving the hospital.

Albert, who is not married, was allowed to succeed his father in 2002 by Monaco’s Constitution although he lacked heirs to become Crown Prince.

Rainier, 81, assumed the throne in 1949 after his grandfather died in 1949. Princess Charlotte, his mother, renounced her claim to the throne in favor of Rainier. He is one of the leaders in reigning.

Rainier III did his best to turn the tiniest country in Europe into a cosy place for the rich.