The private life of the Belgian monarchy has come under fresh scrutiny after King Albert II of Belgium, who abdicated in 2013, was ordered to submit to a DNA test to disprove claims that he conceived a love child during an extramarital affair in the 1960s.

Albert, 84, must provide a saliva sample to the courts within three months or risk being presumed to be the father of the 50-year-old artist Delphine Boël, according to a ruling by the court of appeal in Brussels.

A finding in favour of Boël would lead to the monarch’s estate being split equally between her and the three children he shares with his Italian wife, Queen Paola.

Lawyers for Boël said they welcomed the demand for a sample from the king. “The wound that King Albert struck when he cast her out has not healed,” they said in a statement.

Alain Berenboom, a spokesman for the king, who was on the Belgian throne for 20 years, said his client was taking legal advice on the next steps and any possible grounds of appeal. Albert has denied the paternity claim since it was first made public more than a decade ago.

It has been a difficult year for the Belgian royal family. In March, Prince Laurent, King Albert’s youngest son, claimed his human rights were being violated after the government decided to cut his annual grant. Laurent had been accused of diplomatic freelancing, culminating in an unapproved appearance, in full naval uniform, at a ceremony to mark the 90th anniversary of the founding of China’s People’s Liberation Army.

Among Laurent’s previous forays into deeply political waters were his frequent visits to Libya between 2008 and 2010 during an attempt to go into business with one of Muammar Gaddafi’s sons.

Albert, the son of the wartime king Leopold III, who was criticised by Winston Churchill for surrendering to the Nazis and staying in Belgium after the country’s invasion, abdicated in 2013 for health reasons.

On the same day, Boël’s mother, Baroness Sybille de Selys Longchamps, spoke publicly for the first time about her alleged affair with the king in a television interview.

“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.”

Albert subsequently admitted he and his wife had gone through a marital crisis in the 1970s but the king has never admitted to fathering a love child.

Boël has been seeking official recognition by the king for five years.

Alain De Jonge, who is acting for Boël in the case, said of the latest judgment that the court could not force the king to give a sample.

“No one in our country can be forced to do so but, if he refuses, this can turn out in Albert’s disadvantage because the judge can infer from a wrongful refusal, in combination with other elements of the file, a ‘factual suspicion of fatherhood’,” he said.

Marc Uyttendaele, a second lawyer acting for the claimant, told the Het Nieuwsblad newspaper: “There is so much evidence that Delphine is the daughter of Albert II … We, Delphine Boël’s lawyers, are very pleased with this decision, which is a serene and strong affirmation of the principles that state that the interests of the child should always be given priority.

“This decision is an important step in the difficult battle that Delphine Boël has started after the failure of all amicable steps, so that her identity, and that of her children, is finally legally recognised.”

The current king of the Belgians, Philippe, has not commented.