WHEN most people delve back into their family tree they often find they have surprisingly humble rots.

But one Scottish businessman has uncovered a far more august lineage after being revealed as the direct descendant of one of the kings of Scotland.

A DNA test taken by Archie Shaw Stewart found that he is a distant relative of King Robert III, who reigned from 1390 until his death in 1406, and carries a distinct genetic marker found only in members of his family.

Mr Shaw Stewart is directly descended from one of the king’s sons, Sir John Stewart of Blackhall & Ardgowan, whose great-grandfather fought with Robert the Bruce at Bannockburn.

The findings have been made as part of the Bannockburn Family History Project, which explores genetic connections between people living today and their ancestors who fought in the Battle.

It is run by the Genealogical Studies Postgraduate Programme at Strathclyde’s Centre for Lifelong Learning, and follows a similar discovery by former Prime Minister Gordon Brown, who this week revealed that his own DNA trail had revealed him to be descended from Viking stock.

Graham Holton, Principal Tutor with the programme, said: “This is a fascinating discovery of a distinct marker for descendants of Robert III.

“The marker is not found in descendants of the king’s brothers, showing that a mutation in the DNA occurred in either Robert III himself or one of his descendants.

"It is not yet known in which generation this took place but we are delighted to have been able to confirm Archie Shaw Stewart’s place in medieval royal lineage, and acknowledge his contribution to furthering research into the branches of the Stewarts.”

Mr Shaw Stewart, who runs Scottish electronics company Pan Controls, said: “This is wonderful to be able to discriminate with a high level of confidence between some branches of families by the ability to trace genetic mutations.

“My great uncle, Patrick Shaw Stewart, produced an extensive family tree over 100 years ago, extending back to Robert III. He would be very satisfied to see this part of it verified by new technology.”

Donald Stewart, a retired mechanical engineering draughtsman from Lanark, who also carries the marker, said: “I turned to DNA testing when my genealogy research ran out of documentation and I hit a brick wall. My brick wall was John Stewart, tenant farmer on the Duke of Argyll's estate at High Park, Kintyre, from 1710.

"This discovery, without doubt, confirms tradition and links my High Park family to King Robert III. It has been so worthwhile."

The initial identification of the genetic marker was made by an analyst of genetic data, Alex Williamson.