James Blaesing told a court he wants to establish his ancestry with "scientific certainty".

But other members of Harding's family have opposed the request, filed in May.

They say they have accepted DNA evidence that Mr Blaesing's mother, Elizabeth Ann Blaesing, was the daughter of Harding and Nan Britton.

Harding, the 29th president of the US, had an extramarital affair with Britton before and during his presidency, between 1921 and 1923.

The affair only came to light after Harding died of a heart attack while still in office in 1923.

Britton revealed their relationship in a 1927 book, The President's Daughter, but never sought DNA evidence confirming Harding's paternity of the child. Harding had no other children.

Then in 2015, genetic testing confirmed a match between Mr Blaesing's DNA and that of two Harding descendants. Mr Blaesing's biological link to Harding was officially declared by AncestryDNA, a division of Ancestry.com.