Alexander Armstrong’s posh persona isn’t an affectation. He grew up, he says, “on the edge of quite a grand family, but as second cousins, the junior wing”. Accordingly, he’s certainly not expecting his research to uncover a succession of ladies of the night, as his character did in a Who Do You Think You Are? spoof for The Armstrong & Miller Show. Equally, though, he says he’d be disappointed if he found nothing but “a whole roster of chinless wonders”.

Alexander’s first stop is at his parents’ home, Rothbury. His father’s family has strong associations with the area. “Absurdly, in this modern age, my family still has land,” Alexander says. However, it’s not his father’s forebears that Alexander sets out to trace. Instead, he wants to learn more about his mother Virginia’s ancestors, the McCauslands.

'Absurdly, in this modern age, my family still has land,' Alexander says.

As a child, Alexander remembers visiting the family’s grand country house, Drenagh, in Northern Ireland. It’s such an upper class connection that Alexander is actually listed in Burke’s Landed Irish Gentry. What might he find if he traces back the McCausland line through the years? As it turns out, royal connections and a grisly murder.

Alexander’s 6x great grandmother Mary Boughton (1714-86) was a bedchamber woman to Queen Charlotte – in an era when it was enormously prestigious to hand a chamber pot to royalty. At Shropshire Archives, Alexander sees a picture of Mary, a striking woman. He also sees correspondence that suggests tension between her sons, Edward and Charles. “He is neither fish, flesh, nor good red herring,” Mary writes to Charles of “indolent” Edward, who at one point was more than £14,400 in debt to his younger brother, a colossal sum.

Yet Edward would inherit a title and land when his cousin, Sir Theodosius Boughton was apparently poisoned, a death Edward describes as “wonderful news” in a letter. Could Edward himself be the killer? In fact, Captain John Donnellan, brother-in-law to Theodosius, was convicted of the murder.

A twist in the tale

But there’s still another twist in this tale of sibling rivalry. A few hours before his death, Edward disinherited Charles in favour of his illegitimate daughter. Although dutiful Charles, who married well and was awarded his own baronetcy, inherited his brother’s title, he wasn’t left Edward’s estate. It was a snub that probably cost Sir Charles a peerage.

That’s not to say that Alexander’s family tree lacks for lords and ladies. Via Mary, Alexander’s 9x great grandfather is Henry Somerset, the First Duke of Beaufort (1629-1700). Henry’s father was Edward Somerset, the second Marquess of Worcester (c1601-67). During the English Civil War in the 17th century, this staunch Royalist loaned the equivalent of around £70 million to Charles I.

Sadly, his own war was embarrassingly unsuccessful. Not only did he lead the ‘Mushroom Army’, so called because it sprang up and then disappeared so quickly, but a secret treaty he made on the king’s behalf with Irish Catholics became public knowledge, forcing Charles to imprison his confidant. Edward’s family seat, Raglan Castle, fell to the Parliamentarians.

And yet Edward still emerges from history with huge credit. Why? Because, as Alexander learns at the Science Museum, he was also an inventor, a man regarded as one of the fathers of steam power thanks to his “water-commanding engine”. He was so revered that Victorian engineering enthusiast and collector Bennet Woodcroft (1803-79) even opened up his Edward’s tomb because he hoped to find a model of the engine. Alexander is glad that Edward, who could have been “embittered” by his experiences, instead emerges from history as an inventor and "enthusiast".

Alexander’s final stop is at the College of Arms where, he learns, he’s directly descended from William the Conqueror, which is about as posh as you can get. Alexander is delighted by what he’s found. “From a personal and slightly smug point of view, if I’m entirely honest, there’s something absolutely thrilling about these discoveries,” he says.