The former King Albert II of the Belgians has been ordered by a court to submit to a DNA test or face daily fines of 5,000 euros ($5,600) lawyers said Thursday.
The order was the latest twist in a Belgian's sculptor pursuit to prove that she is the former monarch's daughter.
"I believe that the king will submit to this test since he has the guarantee that it will remain confidential," Albert's lawyer, Guy Hiernaux, told AFP.
Another lawyer, Alain Berenboom, cautioned that the final decision remains with the monarch.
The court-ordered fine was a major development in a long battle between Albert II and Delphine Boel, who launched proceedings before a top Brussels court in 2013 to have Albert's paternity recognized.
Boel claims she was born in 1968 after a long affair between her mother, Sibylle de Selys Longchamps and the then crown prince Albert, married since 1959 to Paola Ruffo di Calabria.
The 81-year-old former monarch, who reigned from 1993 until 2013, has always refused to acknowledge that he could be her father.
Last October, the Brussels Court of Appeal ruled in favor of Boel and ordered Albert II to submit to a genetic sample in order to finally decide the matter.
Albert refused any test, which led to Thursday's order at the appeals court in Brussels.
The ex-king must now report to an appointed forensic expert who, on the basis of a saliva sample, will carry out a comparative analysis with the DNA of Boel and her mother.
After a request made by Boel, the court said the result of the DNA test would remain secret until the end of the legal proceedings, which could last a year.
Boel "herself suggested this option in order to calm the situation and avoid a media storm", her lawyer Marc Uyttendaele told AFP.
"I can't imagine for a second that he (Albert II) doesn't submit to the test," he said.