Alistair Moffat, managing director of BritainsDNA, explained the thinking behind the research:
What we're trying to do is look at Britain and the whole national genome, but everybody is interested in royal DNA.
Royal lineages have been of public interest for centuries. We simply came across this and followed it up. It's a very positive story.
Mr Moffat also researched some of the historical background and found that Theodore Forbes was the third son of a landowning family and had gone to India to seek his fortune.
It was pretty clear to him that he wasn't going to inherit the property, so he came down to Leith (near Edinburgh) and I believe he got involved in the tea business.
He made contact with the East India Company and got himself a job. He went out (to India) as a young Scotsman on the make and it appears he was successful.
That's where he met Eliza and he employed her as his housekeeper. It wasn't uncommon for young British men to have relationships with Indian women.
Mr Moffat said it was "fantastically exciting and unexpected" to uncover such as story in the future king's family tree.
More top news
Rain across much of the remainder of the country
Singer knocks Oasis from their 18-year hold on the top spot as her third album sells more than 800,000 copies in its first week of release
Francois Hollande has urged British MPs to support David Cameron's plan to launch airstrikes against so-called Islamic State in Syria.