A man who believes he may be the illegitimate son of the late Princess Margaret has begun another court battle to access papers relating to her will.
Mr Brown believes Princess Margaret was "forced" to give him up
Jerseyman Robert Brown, 53, was given leave to appeal after the Family Division ruled in July that his claims to see the documents were unfounded.
The Appeal Court later ruled Mr Brown might still have the right to test the principle of sealing royal wills.
Mr Brown believes his father may have been Group Captain Peter Townsend.
Although he was born on 5 January 1955 in Nairobi, Kenya, Mr Brown's birth was not registered until 2 February and the birth certificate gives the date of 4 June 1955.
Research carried out by Mr Brown has convinced him the princess was forced to give up her "secret" son.
He has also said a mystery Privy Council meeting on the day he was born backs up his claim.
If the princess, who died in 2002 aged 71, and the former RAF pilot were Mr Brown's biological parents, the Channel Island accountant would be 12th in line to the throne.
Princess Margaret was engaged to divorced Mr Townsend, but she called off the wedding in October 1955.
The princess said her decision was based on her duty to the Commonwealth and on the Church's teaching that Christian marriage was indissoluble.
Mr Brown's previous attempts to access the wills of Princess Margaret and the Queen Mother have been blocked by judges who say orders to seal the documents should remain in force.
Princess Margaret called off her engagement because of "duty"
But in October, the Court of Appeal ruled it was at least arguable that Mr Brown had standing to assert a general public interest in whether it was right for them to be sealed.
Mr Brown has returned to the appeal court to argue that point before the Lord Chief Justice, Lord Phillips, Lord Justice Thorpe and Lord Justice Dyson.
Geoffrey Robertson QC, representing Mr Brown, said the appeal raised important questions as to the circumstances in which wills - particularly those of the Royal Family - could be sealed and the circumstances in which wills which have been sealed can be unsealed.
Mr Robertson said his client genuinely believed he could be the son of Princess Margaret .
"He wants to inspect the Royal wills as part of his search for the truth about his identity," he said.
Royal wills were made public in the usual way until 1911 when a will was sealed and this had been used as a precedent ever since, said Mr Robertson.
Mr Robertson said there was a heightened need for transparency of the wills of the Royal Family.
He said the Royal Family "enjoys extremely favourable treatment under the Inheritance Tax arrangements" and their wills should be public documents so that the extent to which they are benefiting can be examined.
Mr Brown's appeal is opposed by executors of both estates and the Attorney General, Lord Goldsmith.
Jonathan Swift, who is representing the Attorney General, will argue the Supreme Court has power to allow a will to be sealed.