The Queen, the PM, William IV and his mistress

Updated on 25 May 2010

How royal is David Cameron? Who Knows Who investigates the 13 steps between the Queen and her new prime minister.

A family affair: the Queen, William IV and David Cameron. (Credit: Getty)

If coalition government is all about new bedfellows (in familiar surroundings) then David Cameron has interesting family history which forms an intriguing backdrop to the Queen's Speech.

The most aristocratic prime minister since Sir Alec Douglas Home, Cameron's connection to Her Majesty comes via a sprightly 13 steps in the royal family tree.

The linchpin is William IV, the "sailor king" and the last male of the Hanoverian dynasty.

William IV is the great, great, great granduncle of Queen Elizabeth II.

William IV is the great, great, great, great, great grandfather of David Cameron.

William ruled Britain from 1830 until 1837. He was the third son of George III (whose mental illness was the subject of 1994 film The Madness of King George) and succeeded his brother George IV to become king.

Interestingly, William Pitt, a self-declared "new Tory" was appointed prime minister during George's reign at the age of 24 (following the collapse of a Whig-Tory coalition).

William IV's mother Charlotte of Mecklenburg-Strelitz (Cameron's great, great, great, great, great, great grandmother) was a pen friend of Marie Antoinette and knew Mozart.

William was made Duke of Clarence by his father in 1789 and Clarence House was built for him. It is now the official residence of Prince Charles (but could Cameron come knocking at the door?)

A couple of years later William began a relationship with Dorothea Jordan (nee Bland) which would last 20 years. Because William, one of the younger sons, was not directly in line to the throne his love affair with an actress (and their unmarried status) was not viewed as a problem.

The couple had ten children. It is from this illegitimate line that we find the source of Prime Minister Cameron's blue blood. The children were given the surname FitzClarence (Fitz meaning "son or daughter of").

One of them was Elizabeth FitzClarence (Cameron's great, great, great, great grandmother). She married William Hay, 18th Earl of Erroll and the couple had four children including Lady Agnes Hay.

James Duff, 5th Earl Fife, married Lady Agnes in 1846. They had six children. Five were female - including Lady Agnes Duff. There is another royal union here - the couple's only son Alexander married Princess Louise of Wales, the eldest daughter of Albert Edward, Prince of Wales (later King Edward VII).

Sir Alfred Cooper was a well-respected 19th century surgeon and an expert in treating venereal disease. This specialism gave Sir Alfred (Cameron's great, great grandfather) unusual access to aristocratic and royal circles.

He married Lady Agnes Duff and their daughter Stephanie Agnes Cooper is David Cameron's great grandmother. It is worth noting Stephanie's brother Duff Cooper (like Cameron an old Etonian) was a Conservative politician who served in the cabinet under both Winston Churchill and Stanley Baldwin.

Stephanie married banker Arthur Francis Levita in 1903. The couple had a daughter, Enid Agnes Maud Levita, Cameron's grandmother.

Enid married Ewen Donald Cameron (one of a long line of Ewen Camerons eminent in banking). They had one son - Ian Cameron, David Cameron's father.

Ian married Mary Fleur Mount (herself from aristocratic stock, the daughter of Sir William Mount, 2nd Baronet) in 1962. They have four children including Prime Minister David Cameron who was born in 1966.

This means David Cameron is fifth cousin twice-removed of the Queen.

Meanwhile, the prime minister's wife Samantha Cameron can also trace her lineage to royalty - again via a mistress. An analysis of her family tree reveals that Nell Gwyn, the mistress of Charles II, is Mrs Cameron's great, great, great, great, great, great, great, great grandmother.

It means Samantha Cameron is the Queen's 11th cousin.

Patrick Cracroft-Brennan, from Cracroft's Peerage, told Channel 4 News: "Connections to the Hanoverian and Stuart monarchs are not that common - although that being said Charles II and his brother James II had a lot of illegitimate children and three of our current dukes (Buccleuch, St Albans and Grafton) descend from them."

So can the PM or SamCam make a claim on the throne? Because of the illegitimate nature of their royal roots, the Queen can rest easy for now.