The love child of the former Belgian King Albert II is hoping a court will grant her the same rights and titles as her father’s legitimate children.
Artist Delphine Boël, 52, has taken her case to the appeals court in Brussels.
King Albert finally admitted he was Ms Boël’s father in January this year, having fought her paternity claim for more than a decade.
Her mother, Baroness Sybille de Selys Longchamps, claims she had an 18-year affair with Albert before he was king.
Rumours of an illegitimate child first emerged in 1999 in an unauthorised biography about Albert’s wife Queen Paola, prompting a royal scandal and enduring media gossip in Belgium.
Ms Boël first alleged on the record that King Albert was her biological father during a 2005 interview, but it was not until he abdicated in 2013 – when he lost his immunity to prosecution – that she opened court proceedings.
Her lawyer said on Thursday that she was seeking the same rights as Albert’s three other children, Philippe, now King of Belgium, Prince Laurent and Princess Astrid.
“Delphine’s position isn’t that she wants or doesn’t want to be princess,” said Marc Uyttendaele.
“She doesn’t want to be a cut-price child, she wants to have exactly the same privileges, titles and capacities as her brothers and her sister.”
Reports suggest her children would also be eligible for a royal title if the court rules in her favour.
Albert’s lawyer says she can only be given the title “princess” by royal decree, not by a court.
Baroness Longchamps says the affair with the then Prince Albert of Liège lasted between 1966 and 1984, and he was a presence during Ms Boël’s childhood.
Following his older brother’s death in 1993 at 62, Albert unexpectedly came to the throne.
He held the position until July 2013, when he announced his abdication – citing ill health – and was replaced by his son, Philippe.
The 86-year-old had resisted court orders to undergo DNA testing until he was facing fines of €5,000 per day (£4,611; $5,918, at current exchange rates) for refusing to do so.
In January, he announced he accepted Ms Boël as his fourth child after he “learnt the results of the DNA tests”.
Mr Uyttendaele said at the time the admission was a “relief” for Ms Boël. “Her life has been a long nightmare because of this quest for identity,” he told RTL television.
Belgium has a constitutional monarchy in which the king plays a largely ceremonial role.
Who is King Albert II?
Born in 1934 as second in line to the throne
Married Italian Donna Paola Ruffo di Calabria in 1959
The couple have two sons and a daughter
Became king in August 1993 following the death of his older brother, King Baudouin
With his constitutional role, stepped in during country’s 2010-2011 political stalemate
Served as monarch for two decades until his 2013 abdication