Monaco, April 6 (Reuters): Monaco?s Prince Rainier, whose marriage to US actress Grace Kelly brought Hollywood glamour to his tiny state, died today aged 81.

The palace said Europe?s longest-reigning monarch died at 0435 GMT after a month in hospital battling lung, heart and kidney problems. Some residents of the Mediterranean principality fought back tears as they heard the news, and tributes poured in from foreign leaders for the man who turned Monaco from a faded gambling centre into a billionaires haven.

Rainier put Monaco ? the world?s smallest state after the Vatican ? on the international stage with his romance and then marriage with Kelly in 1956.

Princess Grace died in a car crash in 1982 and Rainier, heartbroken, never remarried. He is expected to be buried beside his wife close to the palace after at least a week?s mourning.

He will be succeeded as ruler of the tiny Mediterranean principality by 47-year-old Prince Albert, who took over his father?s royal duties last week as hopes faded that Rainier would recover.

A shy man, Albert has lived in the shadow of his more glamorous parents and sisters Stephanie and Caroline while being groomed for power as Rainier?s only son.