Many of us daydream about finding royal ancestry, but only a few can boast a blue-blooded lineage leading directly to kings. Much to his surprise and delight, one such soul is four-time Olympic gold medallist Matthew Pinsent.

The royal revelation lies at the end of a Who Do You Think You Are? episode keyed off by Matthew becoming a father and wanting to be able to tell his children about their forebears. “I’d love to find a rogue,” says the rowing champion, “or I’d love to find someone who broke the mold or a complete maverick.”

Instead, his initial research finds tragedy as Matthew looks at the fate of his great uncles during the First World War. On his father’s side, Laurence Pinsent died aged just 19 at Gallipoli. Philip Pinsent was even younger, an 18-year-old pilot who perished in the skies over France. Both attended Winchester College, just two of the thousands of young public schoolboys who saw it as their duty to join up as officers.

Yet did this sense of duty itself carry impossible expectations? Another great uncle, George MacPherson, once Winchester’s head boy, took part in the first ever tank attack at the Somme on 15 September 1916.

Historian Trevor Pigeon tells Matthew what happened when George returned from the fray after a largely unsuccessful attack: “He got out of his tank, he left his crew and he withdrew a short distance. And he took out his revolver and shot himself, the most terrible thing.” We shouldn’t see this as an act of cowardice, adds Trevor, better to see it as an act of misplaced honour in an era of impossible standards.

Matthew’s understandably subdued by his discoveries but he hasn’t time to dwell on what he’s found. He’s soon off to China to research his mother’s great grandfather, David Landale.

In 1907, Landale became both managing director of Jardine Matheson, one of the region’s foremost trading firms and Chairman of the Municipal Council, the body that administered the International Settlement in Shanghai. A man of real influence, Landale lived a life of luxury in pre-revolutionary China.

Yet this luxury was based on opium. The Municipal Council raised a huge percentage of its income from taxing opium dens, while Jardine Matheson was a company built on the proceeds of the, then legal, opium trade. Family legend says that David Landale married into the Jardine family. Family legends, though, can muddle things. While there’s certainly a William Jardine in the family tree, he’s not the William who founded the trading company and sold drugs, but an eminent naturalist. “I think that’s a bit of upgrade,” smiles Matthew.

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A further upgrade lies ahead, keyed off by the discovery of a 'gateway ancestor' in General Sir George Anson (1769-1849), who fought with great distinction during Wellington’s peninsula campaign against Napoleon. Anson was related to the Howard family, allowing Matthew to trace his ancestry directly to Lord William Howard (1510-72), uncle of Katherine Howard, Henry VIII’s fifth wife.

When Katherine was beheaded for adultery, William was imprisoned in the Tower of London. “It’s just chilling,” says Matthew when he visits the Tower, seeing the spot where Katherine was beheaded.

But there are still more surprises, which unfold at the College of Arms. William Howard was descended from Edward I (1239-1307), the Hammer of the Scots and one of the most famous kings in British history. Edward, in turn, was descended from William the Conqueror.

However, at least one of the documents that Matthew views takes things a little too far: a beautiful medieval roll, created at a time when kings claimed to have the divine right to govern, purports to shows the relationship of British monarchy to Jesus, King David, Adam and Eve and even the Supreme Being himself. “At the top of your pedigree,” Matthew is told, “there is God.”