The royal houses of the Lowlands are in a state of upheaval. Two of Europe's most sought-after bachelor princes are about to disappear from the marriage market. After years of despairing over their solitary prince, Belgians are ecstatic at news that Crown Prince Philippe (39) has finally become engaged to a young, highly suitable aristocrat.

However, in the Netherlands the expected engagement of Crown Prince Willem Alexander (31) to his Catholic girlfriend has provoked a whirlwind of speculation about the future of the Protestant House of Orange.

In Belgium, the engagement of the Crown Prince Philippe to Ms Mathilde d'Udekem d'Acoz was officially approved this week by the Belgian government. In the wake of a paedophile affair, a political scandal and a string of food crises, Belgians hope that a royal wedding will present a more positive image of the country abroad. His marriage also puts an end to some 15 years of speculation about the future of the Belgian monarchy.

A speech therapist, Mathilde (26) will become a princess when the couple marry in Brussels on December 4th. She is expected one day to become the seventh queen of the Belgians, but the first who was actually born in Belgium.

The royal household is highly popular among Belgium's 10 million inhabitants. Loyalty towards King Albert II is one of the few things which holds together a nation deeply divided between Dutch and French speakers.

Incredibly, the prince's choice has pleased both the Flemish and the francophones. Mathilde, who comes from a long line of Flemish aristocrats, grew up in the French-speaking south of Belgium.

British newspapers have been quick to draw rather laboured comparisons between Mathilde and the late Diana, Princess of Wales. Like Diana, Mathilde is a tall, blonde and beautiful aristocrat destined to marry a crown prince many years her senior. She has worked with children and has been photographed in a nurse's uniform accompanying invalids to Lourdes.

However, the future Belgian princess, who speaks several languages and runs her own practice, appears to be more mature than Diana at the time of her marriage.

Prince Philippe has denied that his marriage was arranged by the palace. Mr Louis van Raak, editor of the Belgian royal-watching magazine Story, said: "There is real love between Prince Philippe and Mathilde. It is definitely not an arranged marriage."

The royal wedding looks certain to secure the crown prince's place as next in line to the throne. In the past, some commentators suggested that his sister, Astrid, may have succeeded to the throne before the prince because she already has children.

"There has been some hesitation about Prince Philippe but that is finished now. It is not an absolute condition, but it is very important for a king to have a queen," said Mr van Raak.

The forthcoming marriage has not completely silenced media suggestions that Prince Philippe may not have the intellectual capacity to fulfill the duties of a king.

"I never agreed with those insinuations. Philippe is very capable and focused on what he wants to do with his life, but he is restricted by his role as crown prince," said Mr van Raak.

In neighbouring Netherlands, where over 90 per cent of the population is in favour of the monarchy, Prime Minister Mr Wim Kok declared last week that his Labour Party no longer aspires to a future republic.

However, Dutch newspapers have been thrown into a spin by Crown Prince Willem Alexander's relationship with Ms Maxima Zorreguieta. The royal family - the House of Orange - confirmed that the prime minister discussed the relationship with Queen Beatrix and the future heir to the throne at a meeting earlier this month.

"There has been tremendous media coverage, almost to a ridiculous extent," said Dutch author Mr Harry Van Wijnen, who has written several books on the House of Orange. He expects the palace to make an engagement announcement within the next few months.

The prospective bride, Maxima, who works for Dresdner Kleinwort Benson Bank in New York, comes from a Catholic family in Argentina. Her suitability to marry into the Protestant House of Orange has become a hot topic in the Netherlands.

BEFORE the crown prince can marry, he must win approval from the Dutch parliament. The small, minority parties from the religious right could voice objections during the parliamentary vote demanded by the constitution.

"There was a great upheaval in the mid-1960s when Princess Irene, an aunt of Queen Beatrix, became a Catholic and gave up her rights to the throne," explained Mr Van Wijnen. "But today it is unlikely that anyone would take offence, except for two or three very small political groups."

The House of Orange faces another potentially embarrassing problem. Maxima is the daughter of a former minister in the Argentine dictatorship of Gen Videla. The Dutch newspaper, NRC Handelsblad, recalled that the Videla government had been "exceptionally repressive".

In the politically-correct Netherlands, several members of parliament called on Maxima to publicly distance herself from the military regime and officially declare her love for democracy.

"I think that 99 per cent of the parliament will say that the match can go ahead," predicted Mr Van Wijnen. "We can't blame a daughter for the sins of a father."

The irony of a future queen declaring herself to be a full-blooded democrat has not been lost on everyone in the Netherlands.