Routine test reveals white debt collector from Halifax is secret great-great-grandson of last king of the Sikhs

But after a routine test, he has discovered the subcontinent runs in his blood.

The 64-year-old's rare combination of blood groups has revealed he could be related to the last Sikh royal family, who once owned the Koh-i-noor diamond.

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Further research into Mr Goddard's family tree has shown that his great grandfather may have been Prince Freddy, second son of Maharajah Duleep Singh, known as the "last king of the Sikhs".

Mr Goddard, a retired debt recovery officer from Halifax, has been a regular blood donor for years and has the most common type of blood, O-positive.

Tests by the National Blood Service revealed, however, that he also has an unusual combination of minor blood groups, found only in ethnic populations, including Asians and Afro-Caribbeans.

Mr Goddard was unable to explain the discovery until a chance conversation with a cousin gave him the answer.

"I've always been a regular blood donor," he said.

"They check your blood for compatibility with things like transfusions and so they always look at minor blood groupings.

"A doctor telephoned me and told me my blood group was very unusual with factors not seen in white northern Europeans.

"I was subsequently talking to a cousin researching the family tree who told me that there's a bit of a mystery about who our grandfather's parents were."

Mr Goddard said he discovered that his grandfather, Charlie Goddard, who was born in 1888, was the illegitimate son of an unmarried serving maid at Breckles Hall in Norfolk.

"She would never reveal the father's identity, but it was rumoured he was an Indian prince who stayed there," he added.

The story of Mr Goddard's blue bloodline begins with Duleep Singh, who was born in 1838 and proclaimed Maharajah on his fifth birthday.

Unwittingly at the centre of a fierce struggle for control of the Punjab, he lost his kingdom at the age of 11 to the British.

Under the terms of the agreement, he was also forced to surrender ownership of the Sikh religion's most treasured relic, the Koh-i-noor diamond.

One of the world's most famous gems, it was given to Queen Victoria and eventually set in the late Queen Mother's crown.

The Black Prince set up residence in Elveden Hall in Suffolk and in 1864 married the daughter of a German missionary. She bore him three sons and three daughters - none of whom officially had children.

Although Mr Goddard said it was not impossible Duleep Singh is his great-grandfather, the evidence points to his second son Frederick.

Like his father, Freddy was a bachelor and a renowned ladies' man, who lived at Breckles Hall when Charlie was born.

From then on, the Goddard family tree has continued in less colourful fashion.

Mr Goddard was born in Harrow in 1944 and is now a father-of-two.

Asked about his possible links to Indian royalty, he said: "It's interesting, but it doesn't have a real effect on me."

Amy Lansdown-Nasson, of the National Blood Service, said: "We are delighted to have played a part in uncovering Bob's unusual family history and hope his story will inspire more people to become donors."