The husband of Princess Caroline of Monaco, Prince Ernst August of Hanover, has been taken into intensive care with an acute illness of the pancreas.
Prince Ernst August is said to have an acute illness of the pancreas
Princess Caroline's father, Prince Rainier, died only two days ago and his funeral is due to be held on 15 April at the principality's cathedral.
A statement from the royal palace said the prince's condition was serious and he needed constant medical attention.
Doctors are carrying out tests to determine the extent of his illness.
The 51-year-old German prince was taken to the Princess Grace hospital with acute pancreatitis early on Tuesday, the day before Rainier's death, the royal palace said in a statement.
"We are stunned. It is yet another trial for the family," said Monaco's Archbishop Bernard Barsi.
Ernst August and Caroline, 48, the eldest child of Rainier and Hollywood star Grace Kelly, wed in January 1999 in Monaco's royal palace in a civil ceremony.
Together they have a daughter, five-year-old Alexandra, although both have children from previous marriages.
The prince holds joint British and German nationality.
He is the head of the house of Hanover which ruled the UK from 1714 to 1901, but by marrying Caroline - a Catholic - he removed himself from the line of succession to the British throne.
However, he remains the pretender to the throne of Hanover, which was an independent kingdom until 1866.
Prince Rainier, Europe's longest-reigning monarch, died on Wednesday at the age of 81 after spending several weeks in hospital.
He had ruled the tiny principality since 1949 and will be succeeded by his son, Prince Albert, 47.