Javier Sanchez Santos, 41, presented the lawsuit at a court in the Mediterranean city of Valencia where he lives, his lawyer Fernando Osuna, who specialises in paternity suits, told AFP.
Santos' mother, Portuguese ballerina Maria Edite, in 1992 presented a paternity suit against Iglesias but it was eventually dismissed due to procedural reasons.
She says she had a brief affair in 1975 with the Spanish singing legend, who at the time was married to socialite Isabel Preysler.
Now Santos wants to reopen the case based on a DNA test carried out on tissues and cigarette butts touched by Iglesias.
Osuna says the items were collected by a private detective in Miami, where Iglesias now lives.
The test shows there is a 99 percent probability of paternity, the lawyer said.
Santos is "very happy and very satisfied" because "science and genetics have proven that he is right", Osuna said.
"It would be absurd if the court said no to a scientific truth," he added.
If the Valencia court rejects the lawsuit Osuna said he plans to appeal to higher courts in Spain and even up to the European Court of Human Rights in Strasbourg.
Iglesias, 73, has three children with Preysler -- including pop star Enrique -- and five children with his current partner Miranda Rijnsburger.
Known for his romantic ballads and prolific love life that has garnered tabloid headlines, Iglesias is one of the biggest stars of Latin music, with over 300 million albums sold in his decade-long career.