Princess Caroline's husband, Prince Ernst of Hanover, has been taken ill during his annual summer holiday in Ibiza.
On Monday night the 57-year-old royal was rushed to hospital suffering from acute pancreatitis.
Six years ago, the German aristocrat had to be treated in intensive care for the condition, which can be caused by heavy drinking.
He was taken ill one day before the death of his father-in-law Prince Rainier and was unable to attend the funeral.
At the time Ernst, a direct descendant of King George III, vowed to change his lifestyle.
"I don't want (to die) yet. My daughter is only five years old," he said.
Alexandra, his little girl with Caroline, turned 12 on July 20. Ernst wed the princess, who is Albert of Monaco's sister, in 1999.
But their marriage – Caroline's third and his second – has been under scrutiny since they have not been seen together in public for two years.
In fact, Ernst did not even attend the wedding of the Monegasque sovereign to Princess Charlene.