A man claiming to be the illegitimate son of PRINCESS MARGARET is taking the British Royal Family to court over his belief he is 12th in line to the throne. Robert Brown, 51, believes he is the son of Queen Elizabeth II's sister Margaret, who died in 2002 aged 71. He plans to use the Human Rights Act to challenge the rules surrounding the princess' will. Under law, 'sealed' wills like that of Princess Margaret are forbidden to be publicly inspected. Brown was born on 5 January 1955 in Nairobi, Kenya, although his birth certificate shows the much later date of 4 June 1955. His birth mother is listed as CYNTHIA JOAN BROWN. He says, "All I can say is that the pictures of the Princess during 1954 are inconsistent. Certainly in May of that year there are pictures of Princess Margaret where you could put your hand round her waist but throughout the year, the dresses are getting bigger. Around the time of Brown's birth, it was reported that Margaret was confined to bed with what was described as a "hacking cough" - something Brown believes could be conclusive in proving his claim to the throne. However, questions have arisen concerning the authenticity of Brown's claims, especially how a public figure like Princess Margaret could keep a pregnancy hidden. Buckingham Palace refused to accept Brown's earlier offer of a DNA test to prove his royal patronage. A spokesperson for Buckingham Palace says, "While there is a court case pending we can't comment on the matter."