Copenhagen  - Royalists Monday cheered Danish Crown Prince Frederik who turned 40, but turnout was impacted by rainy weather.

The prince, his Australian-born wife Mary and their children Christian and Isabella waved to the crowd from a balcony at Amalienborg Palace in Copenhagen along with Frederik's parents, Queen Margrethe and Prince Henrik.

The crown prince was to stage a party on Saturday for some 100 of his closest friends. However, his newly-wed brother Prince Joachim who married French-born Marie Cavallier over the weekend was to miss out on the party over a honeymoon trip, tabloid Ekstrabladet reported.

After earlier grabbing headlines for his interest in fast cars and sailing, the crown prince appears to be seeking a new role.

Trained as a navy frogman, he in 2000 joined a four-month dog- sledge expedition in the northern part of Greenland and in June was to visit the Arctic island group of Svalbard, off northern Norway with other heirs to the Scandinavian thrones.

"There are so many possibilities of making a contribution, helping out," the prince said in a new biography, Frederik - kronprins af Danmark (Frederik - Crown Prince of Denmark).

In common with other heirs to European thrones, Frederik has also to steer clear of political controversy.

A potentially tricky situation is the ongoing debate over a possible boycott of the opening ceremony at the Beijing Olympics to protest China's human rights record in Tibet.

Calls have been made that the Danish government should stayaway from the ceremony, but if the crown prince follows suit his chances of being elected to the International Olympic Committee (IOC) next year could suffer. (dpa)