Rainier's reign brought a new glamour to Monaco

The prince, who had ruled the tiny Mediterranean principality since 1949, died at 0635 (0435 GMT), the royal palace said.

He had been suffering from heart, kidney and lung problems.

He will be succeeded by Prince Albert, 47 - the son he had by his late wife, former Hollywood star Grace Kelly.

The prince took over his father's royal duties last week.

Affluent haven

A palace statement said Rainier died from the "broncho-pulmonary, heart and kidney conditions that caused his hospitalisation".

RAINIER: KEY DATES 1923: Born in Monaco 1949: Succeeds his grandfather, Prince Louis II 1956: Marries US actress Grace Kelly 1982: Princess Grace dies in a car accident 1999-2005: Several breathing-related operations 7 March, 2005: Hospitalised with lung infection. 6 April, 2005: Dies at age 81 Obituary: Prince Rainier III Life in pictures

The funeral is due to be held on 15 April at the principality's cathedral.

Prince Albert was at his father's side when he died, Reuters news agency reported.

Doctors called him a little before 0600 local time to tell him that the end was near, the palace said.

Rainier had suffered several bouts of bronchitis and undergone several operations in recent years.

He was taken to hospital on 7 March with a lung infection, and moved into intensive care on 22 March.

In 1956, Rainier's reign made headlines when he married Hollywood actress Grace Kelly, who brought a new glamour to Monaco.

It helped the prince turn the principality into an affluent and stylish haven for the rich and famous.

Princess Grace died in a car crash in 1982. They had three children: Caroline, Albert and Stephanie.