Belgium's Queen Paola and King Albert II pose for photographers at the Royal Palace in Laeken, Belgium, in 2008. File picture: Virginia Mayo/AP

Brussels - Belgium's former king Albert II must undergo a DNA test in the next three months to establish whether artist Delphine Boel is his daughter, a court has ruled, according to the Belga news agency.

Boel, 50, has been fighting to be recognized as Albert's daughter since 2013, claiming that her mother, Baroness Sybille de Selys Longchamps, had a lengthy affair with Albert decades ago.

According to Belga, the Brussels appeals court established on October 25 that Jacques Boel, the ex-husband of Delphine Boel's mother, was not her legal or biological father. The decision was made public by Boel's lawyers on Monday.

A DNA test in 2013 established that Jacques Boel was not the artist's biological father. A lower court ruled last year, however, that the paternity suit had no legal basis, as there were other criteria for family ties than biology.

Belgian artist Delphine Boel and her lawyers leave a courthouse, after a new hearing her legal battle to prove former Belgian King Albert is her father, in Brussels

Albert II, who abdicated in 2013 after a 20-year reign, has always denied being Delphine Boel's father, but he has admitted that his marriage to Paola, 81, had been through rocky periods.

The former king could refuse to undergo a DNA test, according to the RTBF broadcaster. If so, the case could be referred to the Court of Cassation, Belgium's highest tribunal.