The illegitimate son of a Dutch prince looks likely to finally be accepted as a member of the royal family after a lengthy legal battle to overturn an informal deal struck at his birth.

Hugo Klynstra, 21, is the son of Prince Carlos, the cousin of King Willem-Alexander, and Brigitte Klynstra, a friend from childhood with whom he had a relationship.

Prince Carlos insists that when Klynstra became pregnant, the couple struck an agreement that the child would receive no royal title or other rights.

The prince has always insisted that his former lover made "an independent decision" to have a child.

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But on reaching the age of 18, Hugo Klynstra decided to challenge that arrangement and has fought a series of legal battles to be granted royal status.

Prince Carlos, Duke of Parma, had a son out of wedlock who was duped of any royal rights. The Duke is pictured here with his wife Annemarie Cecilia Gualtherie van Weezel and their son Carlos Enrique Leonardo Bourbon-Parma. Photo / Getty Images
Prince Carlos, Duke of Parma, had a son out of wedlock who was duped of any royal rights. The Duke is pictured here with his wife Annemarie Cecilia Gualtherie van Weezel and their son Carlos Enrique Leonardo Bourbon-Parma. Photo / Getty Images

He wants the grandiose title of His Royal Highness Prince Carlos Hugo Roderik Sybren de Bourbon de Parme and has also demanded that he be listed in a register of Dutch nobles.

In the latest round of the battle, the matter was discussed on Monday by the Council of State, an advisory body to the Dutch royal family.

The meeting was held behind closed doors, but the council is expected to hand down a decision favourable to Klynstra within a few weeks, according to and other Dutch newspapers.

It would be the end of a legal and constitutional battle that began three years ago, when the 21-year-old mounted the challenge to his father.

Prince Carlos, who is married with three children, has never disputed that Hugo is his son but has remained resolutely opposed to him being given any royal privileges.

King Willem-Alexander of The Netherlands, cousin of Prince Carlos, with his wife Queen Maxima of the Netherlands. Photo / Getty Images
King Willem-Alexander of The Netherlands, cousin of Prince Carlos, with his wife Queen Maxima of the Netherlands. Photo / Getty Images

He has said little about the saga, apart from describing it as "sad and personal".

The prince, who is head of the House of Bourbon-Parma as well as a member of the Dutch royals, appears to be fighting a losing battle – two years ago, the then justice minister, Ard van der Steur, ruled in favour of Klynstra's claim, describing it as valid.

Last year a court in The Hague backed the minister's ruling.

Brigitte Klynstra brought up the boy on her own, although the prince would visit.

Under Dutch law, illegitimate royals are entitled to claim their family's name and titles.