In 90 years, a trial can begin to determine whether Prince Philips' will will continue to be kept secret or not.
More than 30 letters, with sealed wills from deceased British royalty, are in safe custody at the Supreme Court.
The exemption for royal wills was introduced when Francis of Teck, Queen Elizabeth's grandmother's brother, in 1910 passed away and left the Cambridges emeralds, family heirlooms of the Teck family, to his mistress.
His sister then managed to seal the will and buy back the jewels.
Prince Philip, Duke of Edinburgh, died at the age of 99 on Friday 9 April.
Before that, he spent over a month hospitalized for the treatment of a heart defect and an infection.
See the prince's last ride - in a specially designed Land Rover
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On Saturday, the Duke of Edinburgh, Prince Philip, was buried. Even before his death, he had planned a lot for his funeral. Among other things, he has designed the car that will transport his body. Photo: Leon Neal / AP / TT, SVT / EBU