Rapper Juvenile tells TMZ ... he strongly believes he's the biological father of his 13-year-old son ... and claims he only demanded a paternity test as a procedural step to "get custody" of the kid.
Juvenile recently filed court docs, demanding the test ... claiming he never established paternity when his son was born and didn't even sign the birth certificate at the time.
He also claimed the boy's mother has had sexual relations with other people ... so there's a chance he's not the real daddy.
But despite what he said in the court papers, Juv tells TMZ ... "My son acts and looks just like me. I am doing this for procedural reasons to get custody."
What complicated the matter even more ... Juvenile owes $160,000 in unpaid child support ... so if the test proves the kid ISN'T his ... he could be off the hook.
Still, Juvenile tells us he "highly doubts" the test will come back negative ... and says, "I love my son to death ... I hope the test proves that he is mine."