By Alex Dobuzinskis and Steve Gorman

(Reuters) - The administrator of Prince's estate has dismissed claims from three would-be heirs who asserted that their father was also the true biological dad of the late pop star through an alleged affair with his mother.

The denials, in Minnesota court documents filed on Wednesday, came in reply to three individuals seeking a piece of the estate left by Prince after he died unexpectedly in April, apparently without a will, and demanding DNA tests to prove they were his half-siblings.

The dismissals, subject to a judge's review, underscored the tangled and voluminous testaments of kinship that need to be sorted out by the Minnesota probate court overseeing Prince's estate, estimated to be worth more than $500 million.

Among the more colorful are petitions from at least three men claiming they were fathered by Prince out of wedlock - two who are now incarcerated - and a woman who claims she was a secret bride to Prince whose marriage records are classified by the CIA as top secret.

The latest decisions dealt with three people who have asserted that their late father, Loyal James Gresham Jr., was also Prince's biological father by way of an extramarital affair with Prince's mother, Mattie Della Shaw, the year before Prince was born.

Prince, whose legal name was Prince Rogers Nelson, has long been identified in public records as the only son from Mattie Shaw's marriage to John L. Nelson, who also fathered Prince's younger sister, Tyka Nelson, and three older surviving children from a previous marriage.

David Crosby, an attorney for the estate's special administrator, Bremer Trust, wrote in a letter of determination that Minnesota law presumes that John and Mattie were Prince's biological parents because they were married when he was born.

"Only a very limited group of persons have standing to challenge that presumption and, in any event, the time to make such a challenge passed long ago," Crosby wrote.

He cited a statute of limitations requirement that any challenge to that presumption be brought within three years of the child's birth. Prince was born in 1958.

Crosby said no DNA testing was necessary to dismiss the claims of Gresham's three adult children, daughters Darcell Gresham Johnston and Orrine Gresham and son Loyal Gresham III.

Separately, Crosby upheld as valid the claims of heirship from five known half-siblings, previously acknowledged in court filings by Tyka Nelson, who Crosby said have demonstrated that they share at least one genetic parent with Prince.

If Prince left no will and no surviving offspring of his own, as his sister stated, then his estate under Minnesota law would be apportioned in equal shares to his siblings and the nearest surviving descendents of any siblings now dead, according to court papers. Siblings and half-siblings are treated the same under Minnesota inheritance law.

Prince, who was 57, was found dead at his Minnesota home and studio complex in April. Medical examiners ruled last month he died of an accidental, self-administered overdose of the opioid painkiller fentanyl.

(Editing by Cynthia Osterman)