A Kansas City, Mo., man who is serving time in federal prison is claiming to be the biological son of Prince, according to documents filed in Minnesota courts.

In a case filed Monday in Carver County District Court, Carlin Q. Williams said that he is the son of the music superstar and that he is the rightful heir to his estate.

Prince was found dead April 21 in an elevator at his Paisley Park complex in suburban Minnesota. He left no apparent will but his estate is estimated to be worth more than $300 million.

Williams is petitioning for a DNA test to prove that he is actually Prince’s son. It is unclear if or when Minnesota courts will grant his request specifically. In an affidavit filed with the court, a woman named Marsha Henson claims she had unprotected sex in a Kansas City hotel with Prince in July 1976 and gave birth to Williams nine months later.

This is the first case involving Prince claiming paternity since his death, but it comes just days after Judge Kevin Eide, who is overseeing the estate case, ordered genetic testing on a sample of Prince’s blood in anticipation of such claims.

According to Minnesota law, Williams would be first in line to inherit his fortune, even before his siblings who have begun the process of settling his estate.

Currently, Williams is incarcerated until 2020 in federal prison in Florence, Col., for illegally transporting a firearm, according to records.