But there is no doubt: Mr Targett, a 42-year-old history teacher in Cheddar, Somerset, has been shown by DNA tests to be a direct descendant, by his mother's line, of "Cheddar Man", the oldest complete skeleton ever found in Britain, and now also the world's most distant confirmed relative.
Even the Royal Family can only trace its heritage back to King Ecgbert, who ruled from 829AD to 830AD. By contrast, Cheddar Man, a hunter- gatherer who pre-dated the arrival of farming, lived in 7150BC.
The news caught everyone by surprise. Mr Targett's wife, Catherine, said: "This is all a bit of a surprise, but maybe this explains why he likes his steaks rare".
The discovery came about during tests performed as part of a television series on archaeology in Somerset, Once Upon a Time in the West, to be shown later this year. DNA found in the pulp cavity of one of Cheddar Man's molar teeth was tested at Oxford University's Institute of Molecular Medicine, and then compared with that of 20 people locally, whose families were known to have been living in the area for some generations.
To make up the numbers, Mr Targett, an only child who has no children, joined in. But the match was unequivocal: the two men have a common maternal ancestor. The mitochondrial DNA, which is inherited from the egg, confirmed it.
"I'm absolutely overwhelmed," Mr Targett said on hearing of the match. "It is very strange news to receive - I'm not sure how I feel at the moment."
His pupils were delighted ("He has never had a nickname ... until now," one 16-year-old said with relish) and so were scientists. The finding could provide a key to the debate about the process by which early humans settled down to an agricultural life.
Cheddar Man was discovered in 1903, 20 metres inside Gough's cave, which is the largest of 100 caverns in Cheddar Gorge - Britain's prime site for Palaeolithic human remains. He had been buried alone in a chamber near the mouth of a deep cave, about 1,000 years before hunter-gathering began to give way to farming.
Visiting the site, Mr Targett said: "I'm glad I don't live down here - it's very dark, dank and dismal. I have been down here before but, of course, I never dreamed that I was standing in my ancestor's home."
Dr Larry Barham, an archaeology lecturer at Bristol University, said: "There is debate over whether farmers arrived from eastern Europe and ousted the hunter-gatherers - or whether the idea of farm- ing spread through the population. This discovery strongly suggests an element of the second."
In Cheddar Man's time, the area would have been sparsely populated, with dense forests. He would have hunted deer, rabbits, waterfowl and perhaps fish, and gathered nuts, fruit and edible roots. "There were wild boar, bears and beavers. There were packs of wild wolves, too, but apart from that life was probably pretty good. Cheddar Gorge would have looked similar then and must have been a good spot, with ready-made homes, a spring and forest nearby," Dr Barham said.
Physically, Cheddar Man would have looked like modern man. "You could put a suit on him and he wouldn't look out of place in an office. In fact, he probably wore tailored clothes of leather or skins sewn together," Dr Barham added.
"It is likely he was part of an extended group of families of 30 or so people. They lived too late to see a woolly mammoth, and too soon to see the earliest farming."
The link between Cheddar Man and Adrian Targett easily outstrips the existing record for distant ancestors.
The oldest previously recorded relative was the great- great-great-great grandfather of Confucius who lived in the eighth century BC. Two of Confucius's 85th lineal male descendants today live in Taiwan.