You might think that you would not need DNA to test for blue blood. Not so, a Belgian court has decided. The claim by a “royal love child” to establish her lineage can only be tested by modern science.

And so on Monday the court ordered King Albert II (84) to submit DNA – to determine whether he is Delphine Boël’s biological father. He must provide a saliva sample to the courts within three months or risk being presumed to be the father.

Although in Belgium the king is above the law and cannot be arrested, prosecuted or convicted, Albert lost his immunity when he abdicated in 2013, allowing Boel (50), a Belgian visual artist, to then lodge her claim.

If she succeeds in her legal action in proving paternity, she could in theory become 16th in the line of succession to the throne

During the 1960s, the then Prince Albert of Liege, not expecting to be elevated to the throne because his brother Baudouin was first in line, was part of a gilded “jeunesse dorée” wild, rich set and with them spent much of his time sowing his wild oats up on the Cote d’Azur.

At the time of the alleged affair, however, he was married to Paola Ruffo di Calabria, an Italian princess with whom he had three children. Yet during this time Albert had a “long-lasting love affair” with Baroness Sybille de Selys Longchamps, who then gave birth to Boël, according to the latter’s lawyer, Marc Uyttendaele.

Boël’s mother, Baroness Sybille, recently spoke publicly for the first time about her alleged affair with the king in a television interview in which she made clear that the king had privately acknowledged paternity.

Long relationship

“I thought I could not have children because I had had an infection,” she said of the relationship that it is claimed spanned from 1966 to 1984. “We had not taken any precautions.”

“It was a beautiful period. Delphine was a love child. Albert was not the father figure, but he was very sweet to her.”

Belgian artist Delphine Boël: claims former king Albert is her father. Photograph: Francois Lenoir

In 1993, Albert unexpectedly became king after a childless Baudouin died of heart failure at the age of 62. At that point, Albert, it is reported, then severed his connection with Baroness Sybille, and the existence of Boël became a “state secret”, Uyttendaele said. Boël felt rejected, he added.

If she succeeds in her legal action in proving paternity, she could in theory become 16th in the line of succession to the throne, a somewhat distant prospect.

But a finding in her favour would lead to the former monarch’s estate on his death being split equally between her and the three children he shares with his Italian wife, Queen Paola.

Aristocratic name

Asked whether Boël could claim a succession to the Belgian throne, a lawyer for the king, Guy Hiernaux, told the New York Times that “if she’s proven to be his biological daughter, she could hypothetically take his aristocratic name”, Saxe-Coburg and Gotha.

But to become a member of the royal family and claim succession to the throne, she would first need the agreement of the Belgian government – and “we’re not quite there yet”, he said.

The royal family, not least Albert’s son Philippe, who currently sits on the throne and has yet to comment on the alleged affair or its product, will not welcome the renewed attention on members of the clan.

It has not been an easy year – in March, Prince Laurent, King Albert’s youngest son, claimed his human rights were violated after the government decided to cut his annual grant over his unapproved diplomatic “freelancing” in cosying up to the Chinese by attending a reception in full dress uniform.