MINNEAPOLIS -- A legal wrinkle in Prince's estate case shows you might not have to be a blood relative to inherit some of the late rock superstar's sizable fortune.

No will has surfaced since Prince accidentally overdosed on painkillers in April, so his sister, Tyka Nelson, and five half-siblings are likely to be declared rightful heirs within the next few months.

But the judge also has to decide whether a purported niece and grandniece -- plus a purported nephew who came forward this week -- should count as heirs even though they may not be blood relatives. That's because in Minnesota, there are circumstances in which someone can be considered a parent based on having a familial relationship with a child, such as informally raising a non-biological child as their own.

"The statutes don't give clear guidance -- they really don't," said Susan Link, a Minnesota estate law expert who's following the case closely but isn't involved in it.

The judge will have to sort out a complex interplay between probate and parentage laws that appears to be unique to Minnesota, as well as the complicated family history of Prince and his relatives.

Brianna Nelson, her daughter Victoria Nelson and Corey Simmons all claim descent from the late Duane Nelson Sr., who they say was Prince's half-brother. The case filings suggest that Prince's late father, John L. Nelson, might not have been Duane's biological father, but the three allege that John considered Duane to be his son, and that Prince considered Duane to be his half-brother.

Duane's birth certificate lists John Nelson as his father, and John's obituary listed Duane as his son. Duane, who died in 2011, also served as Prince's security chief for several years before they had a falling out.

Should the court count Duane as a half-sibling, Brianna and Victoria Nelson hope to divide what would have been his share (one-seventh) of the estate, which has been estimated at between $100 million and $300 million altogether.

Already, Carver County District Judge Kevin Eide has said Brianna and Victoria have presented a plausible enough case to proceed and don't need to undergo genetic testing.

"One-seventh of the estate after taxes is still a lot of money," Los Angeles probate attorney Robert Straus said.

If Simmons' claim survives, it would be a three-way split. He says Duane Nelson and his mother, Carolyn Simmons, who isn't Brianna Nelson's mother, met at the University of Wisconsin-Milwaukee. Duane left Carolyn when she was five months pregnant and returned to Minnesota, Simmons said. He said his parents' last contact was in 1989, and that he met Brianna and two of Prince's half-sisters for the first time at Duane's funeral.

"His relationship with Brianna Nelson is a happy and affectionate one, in which Brianna Nelson acknowledges him as her brother," Simmons' motion claimed. It also said he attended Prince's family funeral and spent "quality time" there with Brianna and two of Prince's half-sisters he considers his aunts, likely heirs Norrine Nelson and Sharon Nelson.

Little else is known about Simmons. His attorney, Eric Dammeyer, declined to give details, citing privacy concerns.

Lawyers for Brianna and Victoria Nelson argue an extensive revision to the state's probate code 2010 left confusing gaps but that a 2003 Minnesota Supreme Court decision -- issued before that revision -- supports their claims. Lawyers for Bremer Trust, the special administrator overseeing the estate, have countered that it isn't clear whether that's true.

Eide has asked for more written arguments and set dates for two potential hearings in November.