The body of the child, Robert "Bobby" Adam Whitt, was found under a billboard in Orange County back in 1998.
And the child's death remained a mystery until last year.
John Russell Whitt, 57, pleaded guilty Wednesday in an Orange County courtroom to second-degree murder and concealing death.
Whitt was already locked up in a Kentucky prison on an unrelated federal charge.
Whitt is also suspected in the death of Bobby's mother, Myong Hwa, who had been found dead in Spartanburg County, South Carolina, in 1998.