The DNA analysis of saliva samples taken from the Duke of Cambridge's relatives have established a direct lineage between the 30-year-old prince and an Indian housekeeper on his mother Princess Diana's side. (Reuters)

Prince William, second-in-line to the throne, will be first British king with proven Indian ancestry, DNA analysis has revealed.

The DNA analysis of saliva samples taken from the Duke of Cambridge's relatives have established a direct lineage between the 30-year-old prince and an Indian housekeeper on his mother Princess Diana's side.

It is his only non-European DNA and means he will become the first Head of the Commonwealth with a clear genetic link to its most populous nation, India.

William is now likely to be encouraged to make his debut mission to India soon after the birth of his baby next month.

Researchers have uncovered the details of his lineage via a doomed relationship of William's Indian great-great-great-great-great grandmother.

Eliza Kewark was housekeeper to Prince William's great grandfather Theodore Forbes (1788-1820), a Scottish merchant who worked for the East India Company in the port town of Surat in Gujarat.

Eliza's mt DNA was passed on by her daughters and granddaughters directly in an unbroken line to Princess Diana and then on to Prince William and Prince Harry.

Eliza is claimed to have been Armenian, possibly because her surname is rather like the Armenian name Kevork and letters from her to Forbes have been found which contain Armenian script.

This in turn suggests a degree of Armenian cultural heritage and the possibility that her father may have been of Armenian descent.

"But we believe that all the evidence we have gathered shows that her genetic heritage through her motherline is Indian," BritainsDNA, a DNA ancestry testing company, said in a release.

"Princes William and Harry carry Eliza Kewark's markers but will not pass this Indian mtDNA onto their children, as mtDNA is only passed from mother to child," it added.

Jim Wilson, a genetics expert at the University of Edinburgh and BritainsDNA who carried out the tests, said that Eliza's descendants had an incredibly rare type of

mitochondrial DNA (mtDNA), inherited only from a mother.

It has so far been recorded in only 14 other people, 13 Indian and one Nepalese. The revelation explains why the Scottish father of Eliza's children suddenly deserted her and sent their daughter, Katherine, to Britain at the age of six.

Researchers have discovered letters from Eliza to Forbes pleading for her to be allowed to see him.

When Forbes died on a ship back to Britain in 1820 his will referred to Eliza as his "housekeeper" and the mother of his "reputed natural daughter" Katherine.

"Knowing something about your DNA and its origins in prehistory definitely changes your sense of yourself, and one way that it does that is to make you feel part of a world community," said Alistair Moffat, the founder of BritainsDNA.

The researchers also used another type of genetic evidence, autosomal markers, scattered across the genomes of Princess Diana's two matrilineal cousins and compared them to a global database of samples.

"These inherited autosomal markers equate to about 20-50 million letters of DNA out of 6 billion in total. It is therefore very likely that Prince William has not only

inherited a small proportion of Indian DNA from Eliza Kewark but his heirs will also carry it," the researchers concluded.

"I always assumed that I was part-Armenian so I am delighted that I also have an Indian background," said Mary Roach, Princess Diana's maternal aunt who was one of two relatives who provided the DNA samples.

ALSO READ Islamists rally in Egypt ahead of referendum vote, 3 killed

Please read our terms of use before posting comments